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 ...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.展开更多
This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen con...This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen content in both environments,comparative analysis of the annual average oxygen concentration showed that the average inside the forest was 22.13%,while the value outside it was 21.39%.The annual average oxygen concentration inside the forest was 3.34%higher than that outside the forest.(2)Regarding the seasonal variation in oxygen content at both sites,the oxygen concentration inside the forest was consistently higher than that outside the forest in all four seasons.The oxygen concentrations inside the forest were 22.1%,21.9%,21.8%,and 21.5%in spring,summer,autumn,and winter,respectively,while outside the forest,they were 22.0%,21.8%,21.7%,and 21.4%for the same seasons,respectively.(3)The diurnal variation trends of oxygen concentration at both sites were similar throughout all four seasons,exhibiting a single-peak and double-trough curve pattern.The peak period occurred at 13:00 in spring,summer,and winter,and at 9:00 in autumn.The trough periods were observed at 7:00 and between 21:00 and 23:00 or at 5:00.展开更多
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, t...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.展开更多
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 abo...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.展开更多
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...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;.展开更多
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 composit...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.展开更多
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 admi...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.展开更多
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...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.展开更多
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...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℃.展开更多
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 c...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.展开更多
基金Funed by the National Key R&D Program of China(No.2017YFB0309903)
文摘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.
基金Supported by Science and Technology Project of Beijing Municipal Administration Center of Parks (ZX2019ZX2017).
文摘This study was conducted to investigate the air oxygen content inside and outside a Phyllostachys edulis forest in Qishan Forest Park throughout all four seasons.(1)Regarding the overall annual variation in oxygen content in both environments,comparative analysis of the annual average oxygen concentration showed that the average inside the forest was 22.13%,while the value outside it was 21.39%.The annual average oxygen concentration inside the forest was 3.34%higher than that outside the forest.(2)Regarding the seasonal variation in oxygen content at both sites,the oxygen concentration inside the forest was consistently higher than that outside the forest in all four seasons.The oxygen concentrations inside the forest were 22.1%,21.9%,21.8%,and 21.5%in spring,summer,autumn,and winter,respectively,while outside the forest,they were 22.0%,21.8%,21.7%,and 21.4%for the same seasons,respectively.(3)The diurnal variation trends of oxygen concentration at both sites were similar throughout all four seasons,exhibiting a single-peak and double-trough curve pattern.The peak period occurred at 13:00 in spring,summer,and winter,and at 9:00 in autumn.The trough periods were observed at 7:00 and between 21:00 and 23:00 or at 5:00.
基金Project supported by the Foundation of the State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University (Grant No. 0811)the National Natural Science Foundation of China (Grant No. 51009145)the Foundation of Ministry of Education Key Laboratory of High speed ship Engineering, Wuhan University of Technology (Grant No. HSSE 1004)
文摘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.
文摘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.
基金supported by National Natural Science Foundation of China (NSFC) under Grants No. 51407020National Key Technology Research and Development Program of the Ministry of Science and Technology of China under Grants No. 2014BAC13B05Visiting Scholarship of State Key Laboratory of Power Transmission Equipment & System Security and New Technology (Chongqing University) No. 2007DA10512716404
文摘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;.
基金Project(50908229) supported by the National Natural Science Foundation of ChinaProjects(2008G031-N, 50908229, 10125C131) supported by Technological Research and Development Programs of the Ministry of Railways, China
文摘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.
基金Supported by National Natural Science Foundation of China(No.50908229)and the Technological Research and Development Programs of the Ministry of Railways(No.2008G031-N. 2010G004-E)
文摘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.
基金Supported by the International Cooperation Project on the China-Australia Research Centre for Maritime Engineering of Ministry of Science and Technology,China(No.2016YFE0101400)the Basic Scientific Fund for National Public Research Institutes of China(No.2018S03)+4 种基金the National Natural Science Foundation of China(Nos.41821004,41776038)the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1606405)the International Cooperation Project of Indo-Pacific Ocean Environment Variation and Air-Sea Interaction(No.GASI-IPOVAI-05)the IOC/WESTPAC OFS Project,the Ao Shan Talents Cultivation Excellent Scholar Program Supported by Qingdao National Laboratory for Marine Science and Technology(No.2017ASTCP-ES04)the China-Korea Cooperation Project on the Prediction of North-West Pacific Climate Change
文摘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.
文摘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℃.
文摘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.
