The Influence of Atmospheric Pressure on Air Content and Pore Structure of Air-entrained Concrete

To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.

EXPERIMENTAL STUDY OF EFFECTS OF AIR CONTENT ON CAVITATION AND PRESSURE FLUCTUATIONS

This article studies the effects of air content on propeller cavitation and pressure fluctuations. The cavitation is observed while the pressure fluctuations on the hull are measured. When adjusting the air content, the sheet cavitation range does not change distinctly, but the pressure fluctuations see obvious differences. The amplitudes of the pressure fluctuations increase with the decrease of the air content. The results indicate that the air content has little effect on the sheet cavitation range but has an important effect on the bubble cavitation and the tip vortex cavitation. When the air content decreases, the water tensile force increases, which results in the instability of the bubble cavitation and the tip vortex cavitation and the increase of the pressure fluctuations. To minimize the scale effects, the experiments should be run at a high Reynolds number with a high nuclei content. The high Reynolds number is often realized by increasing the flow velocity and the propeller rotation speed, and the high nuclei content is often made by increasing the dissolved air content.

^7Be content and its seasonal variation in the ground air around Hangzhou area

Twice investigations around Hangzhou area show that ^7Be content average in the ground air is 5.9mBq.m^-3.The content of ^7Be is the highest in autumn-winter period reaching about 7.7mBq.m^-3,the next is in spring about 6.2mBq.m^-3.then is in the early summer about 5.7mBq.m^-3,close to the annual average level;and the lowest in a year is in summer-autumm period with a value about 3.8mBq.m^-3.Exhibited is a decreasing trend from autumn-winter period to summer-autumn of the next year,which is negatively correlated with the variation of the seasonal rainfall in Hangzhou area.But this trend is different from that reported by UNSCEAR:it is the highest in spring and the lowest in the late autumn,which is based only on ^7Be falling down from the stratosphere.However,the present investigation shows that the seasonal rainfall is the main factor influencing the variation tend of ^7Be content in the air.

Influence of water content on the inactivation of P. digitatum spores using an air–water plasma jet

In order to investigate whether an air–water plasma jet is beneficial to improve the efficiency of inactivation, a series of experiments were done using a ring-needle plasma jet. The water content in the working gas（air） was accurately measured based on the Karl Fischer method. The effects of water on the production of OH（A;Σ;–X;Π;） and O（3p;P–3s;S） were also studied by optical emission spectroscopy. The results show that the water content is in the range of 2.53–9.58 mg l;, depending on the gas/water mixture ratio. The production of OH（A;Σ;–X;Π;） rises with the increase of water content, whereas the O（3p;P–3s;S） shows a declining tendency with higher water content. The sterilization experiments indicate that this air–water plasma jet inactivates the P. digitatum spores very effectively and its efficiency rises with the increase of the water content. It is possible that OH（A;Σ;–X;Π;） is a more effective species in inactivation than O（3p;P–3s;S） and the water content benefit the spore germination inhibition through rising the OH（A;Σ;–X;Π;） production. The maximum of the inactivation efficacy is up to 93% when the applied voltage is -6.75 kV and the water content is 9.58 mg l;.

水工调蓄水池池壁混凝土预制板外观质量试验研究

为兼顾混凝土外观质量与耐久性,基于宁夏扁担沟扬水灌区吴家沟调蓄水池工程,研究了减水剂类型、引气剂类型和脱模剂类型对池壁混凝土预制板外观质量的影响。结果表明,掺入萘系减水剂的试件外观质量明显优于掺入聚羧酸减水剂的试件;掺入松香类、AOS和三萜皂甙引气剂的试件外观质量明显优于掺入醚类引气剂的试件;在保证混凝土力学性能和耐久性的前提下,适当增大水胶比,减小混凝土黏度,有利于气泡的排出;喷涂水性脱模剂浓度为0.05%~0.10%时,试件表面平整光洁,几乎无气泡,工程应用效果良好。

基于地铁车辆空压机出口压力空气含水量影响因素分析的正交试验设计方法

[目的]地铁列车空压机出口压力空气干燥度是一个非常重要的指标。如果压力空气中含水量高,就会影响各用风设备的性能,进而影响行车安全。上海轨道交通运维人员在汛期对某些线路列车进行检修时发现,列车供风管路中存在液态水,这是因压力空气中含水量过高而造成的。需要在现有条件下,研究如何调整维修策略,进而改善空压机在汛期的干燥能力。[方法]通过正交试验设计方法,设计了用于分析空压机出口压力空气含水量影响因素的试验方案,给出了使用田口方法分析数据进而确定主要影响因素的方法。[结果及结论]运用该试验方案进行试验,能够分析出影响列车空压机出口压力空气含水量的主要因素,运维人员可据此结论制定适用于汛期的列车空压机维修策略。该正交试验设计方法也可以推广应用至城市轨道交通其他设备运维策略的完善与优化工作之中。

Air-void parameters measurement of fresh concrete and hardened concrete

Air content, spacing factor and specific surface of fresh concrete and hardened concrete with different air contents, slumps and mineral admixtures (fly ash, slag, fly ash + slag, fly ash + slag + silica fume composite) were studied by the air-void analyzer (AVA) method and the microscopical method. The correlations between the test results obtained from different methods were analyzed. The results show that, there is a close correlation of air content and spacing factor between the fresh concrete and the hardened concrete, but the specific surface correlation is weak. The air content of concrete measured by the AVA method is smaller than that of the pressure method and the microscopical method, because AVA device captures only the air voids with the size smaller than 3 mm. Spacing factor of the fresh concrete measured by the AVA method is greater than that of the hardened concrete measured by the microscopical method, while the specific surface is smaller. When the criterion of 4%-7% air content measured by the pressure method and microscopical method is acceptable for concrete freezing-thawing (F-T) durability in cold weather, the air content measured by the AVA method should be 2.4%-4.6%. For the concrete F-T durability, when the criterion of the spacing factor measured by the microscopical method is 300 μm, the spacing factor measured by the AVA method should be 360 μm.

Air-void Parameters Measurement of Fresh Concrete

To explore the method to evaluate air-void parameters of fresh concrete rapidly, the spacing factor and specific surface of freshly mixed concrete of different air contents, different slumps and different mineral admixtures （fly ash, fly ash-slag, fly ash-slag-silica fume composite） are studied by air-void analyzer （AVA）, and the correlation between the air content measured by AVA and air content determinator is compared. The results show that the spacing factor of the fresh concrete decreases firstly and then increases with the increase of air content, however the specific surface has the opposite rule. When the air content is more than 8%, the spacing factor of fresh concrete increases and the specific surface decreases. For the fresh concrete samples with similar air content, the specific surface increases firstly and then decreases with the increase of slump, but the spacing factor decreases firstly and then increases. Mineral admixalre can reduce the spacing factor of fresh concrete and increase the specific surface to some degree. There is a good correlation between the air content measured by two methods, and the air content measured by AVA is about 70% of the air content measured by the air content determinator.

鸡ADSL基因和GARS-AIRS-GART基因对鸡肉肌苷酸(IMP)含量的影响

以鸡ADSL基因、GARS-AIRS-GART基因为侯选基因,以隐性白羽鸡、丝羽乌骨鸡、萧山鸡、白耳鸡、藏鸡为试验材料,采用PCR-SSCP方法对ADSL外显子2、GARS-AIRS-GART基因5′侧翼序列进行SNPs检测。结果各发现了一个单核苷酸多态性位点。各种基因型与胸肌IMP含量的最小二乘分析结果表明:ADSL基因TT型个体的胸肌肌苷酸含量极显著地高于CC型、显著地高于CT型个体,CT型个体也高于CC型,但差异不显著;GARS-AIRS-GART基因TT型个体的胸肌肌苷酸含量极显著地高于CT型和CC型个体,CT型个体也高于CC型,但差异不显著。ADSL和GARS-AIRS-GART基因的合并基因型对IMP含量也有显著的影响,合并基因型为TTTT的个体IMP含量显著高于CCCC合并基因型的个体,高出1.584 mg/g,因此可以利用该合并基因型对鸡的肉质风味性状进行标记辅助选择。

低温条件下糙米储藏品质和微观结构变化的研究

以3种不同初始含水量(13.5%、15.5%、17.9%)的糙米为研究对象,在低温15℃储藏下,对比10%O2+90%N2气调组和空气自然密封组,研究低温条件下不同含水量糙米储藏品质和微观结构的变化。结果表明:低温15℃储存的糙米,含水量越高,则脂肪酸值越大,发芽率越低,食味值越小,微观结构越差;低温气调储藏能延缓糙米脂肪酸值的上升和发芽率的降低,在一定程度上可保持糙米的品质,可为糙米保质保鲜储藏提供新方案。

乳胶枕物理性能影响因素的研究

乳胶枕头因具有舒适性的特点与有益于身体健康的作用而备受消费者青睐。乳胶枕头的物理性能是衡量其质量品质的重要指标之一。设计实验探讨影响乳胶枕头物理性能的关键因素。结果显示:苯乙烯和4苯基环己烯在多个样品中被检出,但含量相对较低;乳胶枕样品在N亚硝基胺测试中均未检出;pH值均在6.7~7.3之间,呈中性或弱酸性范围,8个乳胶枕样本中的铬含量未检出,3#、4#、7#、10#、12#、14#样本检测到了铬的存在,未超过安全阈值;铅的含量均较低,最高为35.6 mg/kg(14#),均在安全范围之内。为乳胶枕头的生产与质量控制提供了有价值的参考信息。

双真空过滤机在尾矿脱水方面的应用

选矿厂现用尾矿库库容严重不足,为了减少尾矿入库量,延长尾矿库使用年限,借鉴双真空盘式过滤机在精矿脱水方面的良好应用效果,开展了双真空盘式过滤机在尾矿脱水方面的研究及应用。双真空盘式过滤机与带式真空过滤机和压滤机实验对比,在装机数量、过滤系数、滤饼水分、占地面积、设备价格等多方面指标占优,脱水工艺相对简单,操作方便,日常维护点少,是最优脱水设备。

Investigation of gas content of organic-rich shale:A case study from Lower Permian shale in southern North China Basin,central China

Measuring gas content is an essential step in estimating the commerciality of gas reserves. In this study,eight shale core samples from the Mouye-1 well were measured using a homemade patented gas desorption apparatus to determine their gas contents. Due to the air contamination that is introduced into the desorption canister, a mathematical method was devised to correct the gas quantity and quality.Compared to the chemical compositions of desorbed gas, the chemical compositions of residual gas are somewhat different. In residual gas, carbon dioxide and nitrogen record a slight increase, and propane is first observed. This phenomenon may be related to the exposure time during the transportation of shale samples from the drilling site to the laboratory, as well as the differences in the mass, size and adsorptivity of different gas molecules. In addition to a series of conventional methods, including the USBM direct method and the Amoco Curve Fit(ACF) method, which were used here for lost gas content estimation, a Modified Curve Fit(MCF) method, based on the 'bidisperse' diffusion model, was established to estimate lost gas content. By fitting the ACF and MCF models to gas desorption data, we determined that the MCF method could reasonably describe the gas desorption data over the entire time period, whereas the ACF method failed. The failure of the ACF method to describe the gas desorption process may be related to its restrictive assumption of a single pore size within shale samples. In comparison to the indirect method, this study demonstrates that none of the three methods studied in this investigation(USBM, ACF and MCF) could individually estimate the lost gas contents of all shale samples and that the proportion of free gas relative to total gas has a significant effect on the estimation accuracy of the selected method. When the ratio of free gas to total gas is lower than 45%, the USBM method is the best for estimating the lost gas content, whereas when the ratio ranges from 45% to 75% or is more than 75%, the ACF and MCF methods, are the best options respectively.

Contribution of surface wave-induced vertical mixing to heat content in global upper ocean

Compared with observations,the simulated upper ocean heat content(OHC)determined from climate models shows an underestimation bias.The simulation bias of the average annual water temperature in the upper 300 m is 0.2℃lower than the observational results.The results from our two numerical experiments,using a CMIP5 model,show that the non-breaking surface wave-induced vertical mixing can reduce this bias.The enhanced vertical mixing increases the OHC in the global upper ocean(65°S–65°N).Using non-breaking surface wave-induced vertical mixing reduced the disparity by 30%to 0.14℃.The heat content increase is not directly induced by air-sea heat fluxes during the simulation period,but is the legacy of temperature increases in the first 150 years.During this period,additional vertical mixing was initially included in the climate model.The non-breaking surface wave-induced vertical mixing improves the OHC by increasing the air-sea heat fluxes in the first 150 years.This increase in air-sea heat fluxes warms the upper ocean by 0.05–0.06℃.The results show that the incorporation of vertical mixing induced by nonbreaking surface waves in our experiments can improve the simulation of OHC in the global upper ocean.

Hot Air Drying and Quality of Red and White Varieties of Onion (Allium cepa)

This study was undertaken to investigate the drying characteristics of red and white varieties of onion (Allium cepa) in a convective dryer. The drying characteristics of onion slices were examined at air temperatures of 50℃, 60℃ and 70℃ and sample thicknesses of 2 mm. During the drying experiments, air velocity was held stable at 0.9 m/s. The effects of air temperature on the drying characteristics and quality parameters such as vitamins C and D, macro minerals (Mg, Na, P, Ca and K), non-enzymatic browning and thiolsulphinate of the dried onion slices were determined. For each of the plots of the drying curves from the mechanical drying tests, there was an absence of or just a very brief appearance of a constant rate period because onions are hygroscopic and hygroscopic foods tending to quickly enter the falling rate period;drying time decreased considerably with increased temperature. The time required to reduce the moisture content to any given value was dependent on the drying conditions, being the longest at an air temperature of 50℃, 0.9 m/s and the shortest at an air temperature of 70℃ and air velocity of 0.9 m/s. The loss of vitamin C, which is a thermo-sensitive compound, was the least at an air temperature of 50℃.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

The quantitative effects of chromium content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.

杭州国家版本馆恒温恒湿空调系统设计

介绍了恒温恒湿库房空调系统的设计,提出了可在库房建成初期、运行稳定期、战时等灵活切换的3种运行模式,分析了其各自的处理过程与节能性;给出了平、战时空调系统选择方案,提出了平时回收空气源热泵机组和冷水机组的冷凝热作为再热热源,战时利用新风预冷实现温湿度独立控制的方法;利用CFD模拟对室内气流组织进行了优化设计;提出了采用含湿量控制代替定露点法进行湿度控制和风机变频等控制策略。通过调试与运行,证明了各项设计措施在项目中应用的有效性。

“车辆制冷与空气调节”课程教学改革探讨

分析“车辆制冷与空气调节”课程的特点,并结合该课程在教学中存在的问题,探讨了在教学改革过程中采取的措施:整合教学内容、改进教学方法和手段、调整教学环节及加强实验室建设等。在师生共同努力下,课程教学得到了不断改进和优化,学生普遍反映课程内容设计合理、思政案例丰富、学习过程充实,自身专业素质和创新设计能力得到了提高,对人生观和价值观有了更加深入的思考,取得了良好的教学效果。

木材气干密度与基本密度关系模型比较

木材密度包括基本密度、气干密度等,在12%含水率条件下的气干密度(D12)较常用,因此有必要将木材气干密度换算为基本密度(Db)。目前利用木材气干密度计算基本密度的模型有Reyes、Chave、Simpson和Vieilledent模型等,然而这些模型预测结果不完全一致。利用中国林业科学研究院木材工业研究所(Research Institute of Wood Industry,Chinese Academy of Forestry,CRIWI)和法国农业国际合作研究发展中心(French Agricultural Research Centre for International Development,CIRAD)的木材D12和Db数据,首先基于CRIWI的木材密度数据建立D12与Db的关系模型,然后将CRIWI和CIRAD的D12数据分别代入Reyes模型、Chave模型、Simpson模型、Vieilledent模型和新建模型,获得每个树种木材Db的预测值,并根据Db预测值和实测值计算残差绝对值均值。不同模型残差绝对值均值比较结果表明:Reyes模型在利用CRIWI和CIRAD的木材密度数据时预测Db的准确性都比较高,适用性最广;Simpson模型、新建模型在D12高于1.0 g/cm3时预测Db的准确性降低。