The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase st...The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140℃and poling time of 20-25 min.展开更多
O437 2000031758极化光纤中二阶非线性效应的检测=Detection ofsecond order nonlinear effects in poled opticalfibers[会,中]/熊水东,陈哲,胡永明,郑贤旭,周沐(国防科技大学二系.湖南,长沙(410073))//全国第九次光纤通信暨第十届集...O437 2000031758极化光纤中二阶非线性效应的检测=Detection ofsecond order nonlinear effects in poled opticalfibers[会,中]/熊水东,陈哲,胡永明,郑贤旭,周沐(国防科技大学二系.湖南,长沙(410073))//全国第九次光纤通信暨第十届集成光学学术会议.—秦皇岛,99.08对长6cm的光纤进行极化,并测试其二阶非线性效应,通过实验对比,提供优化光纤极化条件的数据,从而提高其二阶非线性系数。(赵桂云)展开更多
Study of electrochemical behavior of chromium （molybdenum, tungsten） and silicon containing melts allowed defining conditions for synthesis of silicides of chromium, molybdenum and tungsten in the form of fine powde...Study of electrochemical behavior of chromium （molybdenum, tungsten） and silicon containing melts allowed defining conditions for synthesis of silicides of chromium, molybdenum and tungsten in the form of fine powders by electrolysis of halide-oxide melts. Sequence of stages of electrosynthesis of silicides of molybdenum and tungsten was found as follows： deposition of more electroposifve metal （molybdenum or tungsten）, deposition of the second component （silicon） on the surface of metal deposited previously, and reaction diffusion of silicon into the deep of the metal-salt ＂pear＂ with the formation of silicide phases of different compositions up to the higher silicides. In contrast, during the electrodeposition of chromium silicides, one of the components （chromium） is deposited not in elemental form, but in oxide form, and the other （silicon） acts as a reducing agent for this oxide to form binary compounds. Duration of the synthesis first stage （deposition of refractory metal or of its oxide） depends on the refractory metal compound content in the system and on the cathode current density. Synthesis of silicides is possible due to retention of powders of molybdenum （tungsten） or chromium oxide at the cathode without scaling. Optimal values of concentrations ratio, current density, temperature, and duration of electrosynthesis were found. Phase composition of products were obtained, as well as their chemical and thermal stability, were studied.展开更多
This paper presents the influence of solvent polarity and extraction conditions on the extraction of total flavonoid, total phenolic and antioxidants from Averrhoa bilimbi. The experiment was performed using a differe...This paper presents the influence of solvent polarity and extraction conditions on the extraction of total flavonoid, total phenolic and antioxidants from Averrhoa bilimbi. The experiment was performed using a different solvent at different extraction conditions, including extraction time （15-240 min）, temperature （30-70 ℃） and agitation speed （50-300 rpm）. Results showed that yields of extraction varies with solvent polarity. Extraction using 50% aqueous methanol gives the highest antioxidant activity and flavonoid content. The highest total flavonoid content （193.3 μg quercetin equivalent/g dry weight）, total phenolic content （717.8 μg gallic acid equivalent/g dry weight） and antioxidant activity （77%） was achieved using 50% methanol, at 70 ℃ and agitation speed of 300 rpm. This work may be useful for obtaining higher bioactive compounds during the extraction process of A. bilimbi.展开更多
Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline medium are of significance f...Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline medium are of significance for producing clean fuel to relieve energy and environment crisis.Here,a novel Ni/NiO monolithic electrode was developed by a facile and cost-effective acid promoted activation of Ni foam.After the treatment,this obtained monolithic electrode with a layer of NiO on its surface demonstrates rough and sheet-like morphology,which not only possesses larger accessible surface area but also provides more reactive active sites. Compared with powder catalysts,this monolithic electrode can achieve intimate contact between the electrocatalyst and the current collector,which will alleviate the problem of pulverization and enable the stable function of the electrode. It can be served as an efficient bi-functional electrocatalyst with an overpotential of 160 mV for HER and 290 mV for OER to produce current densities of 10 mA cm^（-2） in the alkaline medium. And it maintains benign stability after 5,000 cycles,which rivals many recent reported noble-metal free catalysts in 1.0mol L^（-1） KOH solution. Attributed to the easy,scalable methodology and high catalytic efficiency,this work not only offers a promising monolithic catalyst but also inspires us to exploit other inexpensive,highly efficient and self-standing noble metalfree electrocatalysts for scale-up electrochemical water-splitting technology.展开更多
Solar evaporation has emerged as an attractive technology to produce freshwater by utilizing renewable solar energy.However,it remains a huge challenge to develop efficient solar steam generators with good flexibility...Solar evaporation has emerged as an attractive technology to produce freshwater by utilizing renewable solar energy.However,it remains a huge challenge to develop efficient solar steam generators with good flexibility,low cost and remarkable salt resistance.Herein,we prepare flexible,robust solar membranes by filtration of porous carbon and commercial paper pulp fiber.The porous carbon with well-defined structures is prepared through controlled carbonization of biomass/waste plastics by eutectic salts.We prove the synergistic effect of porous carbon and paper pulp fiber in boosting solar evaporation performance.Firstly,the porous carbon displays a high light absorption,while the paper pulp fiber with good hydrophilicity effectively promotes the transport of water.Secondly,the combination between porous carbon and paper pulp fiber reduces the water vaporization enthalpy by 20%,which is important to significantly improve the evaporation performance.As a proof of concept,the porous carbon/paper pulp fiber membrane possesses a high evaporation rate of 1.8 kg m^(-2)h^(-1)under 1 kW m^(-2)irradiation.Thirdly,the good flexibility and mechanical property of paper pulp fiber enable the solar membrane to work well under extreme conditions(e.g.,after 20 cycles of folding/stretching/recovery).Lastly,due to the super-hydrophilicity and superwetting,the hybrid membrane exhibits the exceptional salt resistance and long-term stability in continuous seawater desalination,e.g.,for 50 h.Importantly,a large-scale solar desalination device for outdoor experiments is developed to produce freshwater.Consequently,this work provides a new insight into developing advanced flexible solar evaporators with superb performance in seawater desalination.展开更多
The effect that climatic changes can exert on parasitic interactions represents a multifactor problem whose results are difficult to predict. The actual impact of changes will depend on their magnitude and the physiol...The effect that climatic changes can exert on parasitic interactions represents a multifactor problem whose results are difficult to predict. The actual impact of changes will depend on their magnitude and the physiological tolerance of affected organisms. When the change is considered extreme （i.e. unusual weather events that are at the extremes of the historical distribution for a given area）, the probability of an alteration in an organisms＇ homeostasis increases dramatically. However, factors determining the altered dynamics of host-parasite interactions due to an extreme change are the same as those acting in response to changes of lower magnitude. Only a deep knowledge of these factors will help to produce more accurate predictive models for the effects of extreme changes on parasitic interactions. Extreme environmental conditions may affect pathogens directly when they include free-living stages in their life-cycles and indirectly through reduced resource availability for hosts and thus reduced ability to produce efficient anti-parasite defenses, or by effects on host density affecting transmission dynamics of diseases or the frequency of intraspecific contact. What are the consequences for host-parasite interactions？ Here we summarize the present knowledge on three principal factors in determining host-parasite associations; biodiversity, population density and immunocompetence In addition, we analyzed examples of the effects of environmental alteration of anthropogenic origin on parasitic systems because the effects are analogous to that exerted by an extreme climatic change [Current Zoology 57 （3）： 390405, 2011].展开更多
It is difficult to judge whether a given point is a global maximizer of an unconstrained optimization problem. This paper deals with this problem by considering global information via integral and gives a necessary an...It is difficult to judge whether a given point is a global maximizer of an unconstrained optimization problem. This paper deals with this problem by considering global information via integral and gives a necessary and sufficient condition judging whether a given point is a global maximizer of an unconstrained optimization problem. An algorithm is offered under such a condition and finally two test problems are verified via the offered algorithm.展开更多
Extreme weather conditions occur at an increasing rate as evidenced by higher frequency of hurricanes and more extreme precipitation and temperature anomalies. Such extreme environmental conditions will have important...Extreme weather conditions occur at an increasing rate as evidenced by higher frequency of hurricanes and more extreme precipitation and temperature anomalies. Such extreme environmental conditions will have important implications for all living organisms through greater frequency of reproductive failure and reduced adult survival. We review examples of reproductive failure and reduced survival related to extreme weather conditions. Phenotypic plasticity may not be sufficient to allow adaptation to extreme weather for many animals. Theory predicts reduced reproductive effort as a response to increased stochasticity. We predict that patterns of natural selection will change towards truncation selection as environmental conditions become more extreme. Such changes in patterns of selection may facilitate adaptation to extreme events. However, effects of selection on reproductive effort are difficult to detect. We present a number of predictions for the effects of extreme weather conditions in need of empirical tests. Finally, we suggest a number of empirical reviews that could improve our ability to judge the effects of extreme environmental conditions on life history [Current Zoology 57 （3）： 375-389, 2011].展开更多
基金Project(10474077) supported by the National Natural Science Foundation of China Project(2002CB613304) supported by the National Basic Research Program of China
文摘The lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 (abbreviated as KNN) with the relative density of 97.6% were synthesized by press-less sintering owing to the careful control of processing conditions. The phase structure of KNN ceramics was analyzed. The results show that the pure perovskite phase with orthorhombic symmetry is in all ceramics specimens. The effect of poling conditions on the piezoelectric properties of KNN ceramics was investigated. The results show that the piezoelectric constant d33 and electromechanical coupling factor kp increase with poling field, poling temperature and poling time increasing, then decrease because of electric broken. Take into account of poling conditions and piezoelectric properties of pure KNN ceramics, the optimum poling conditions for pure KNN ceramics are poling field of 4 kV/mm, poling temperature of 140℃and poling time of 20-25 min.
文摘O437 2000031758极化光纤中二阶非线性效应的检测=Detection ofsecond order nonlinear effects in poled opticalfibers[会,中]/熊水东,陈哲,胡永明,郑贤旭,周沐(国防科技大学二系.湖南,长沙(410073))//全国第九次光纤通信暨第十届集成光学学术会议.—秦皇岛,99.08对长6cm的光纤进行极化,并测试其二阶非线性效应,通过实验对比,提供优化光纤极化条件的数据,从而提高其二阶非线性系数。(赵桂云)
文摘Study of electrochemical behavior of chromium （molybdenum, tungsten） and silicon containing melts allowed defining conditions for synthesis of silicides of chromium, molybdenum and tungsten in the form of fine powders by electrolysis of halide-oxide melts. Sequence of stages of electrosynthesis of silicides of molybdenum and tungsten was found as follows： deposition of more electroposifve metal （molybdenum or tungsten）, deposition of the second component （silicon） on the surface of metal deposited previously, and reaction diffusion of silicon into the deep of the metal-salt ＂pear＂ with the formation of silicide phases of different compositions up to the higher silicides. In contrast, during the electrodeposition of chromium silicides, one of the components （chromium） is deposited not in elemental form, but in oxide form, and the other （silicon） acts as a reducing agent for this oxide to form binary compounds. Duration of the synthesis first stage （deposition of refractory metal or of its oxide） depends on the refractory metal compound content in the system and on the cathode current density. Synthesis of silicides is possible due to retention of powders of molybdenum （tungsten） or chromium oxide at the cathode without scaling. Optimal values of concentrations ratio, current density, temperature, and duration of electrosynthesis were found. Phase composition of products were obtained, as well as their chemical and thermal stability, were studied.
文摘This paper presents the influence of solvent polarity and extraction conditions on the extraction of total flavonoid, total phenolic and antioxidants from Averrhoa bilimbi. The experiment was performed using a different solvent at different extraction conditions, including extraction time （15-240 min）, temperature （30-70 ℃） and agitation speed （50-300 rpm）. Results showed that yields of extraction varies with solvent polarity. Extraction using 50% aqueous methanol gives the highest antioxidant activity and flavonoid content. The highest total flavonoid content （193.3 μg quercetin equivalent/g dry weight）, total phenolic content （717.8 μg gallic acid equivalent/g dry weight） and antioxidant activity （77%） was achieved using 50% methanol, at 70 ℃ and agitation speed of 300 rpm. This work may be useful for obtaining higher bioactive compounds during the extraction process of A. bilimbi.
基金supported by the National Natural Science Foundation of China (21571073 and 21673090)the National Basic Research Program of China (2015CB932600)+2 种基金Hubei Provincial Natural Science Foundation of China (2016CFA031)the Program for HUST Interdisciplinary Innovation Team (2015ZDTD038)the Fundamental Research Funds for the Central Universities
文摘Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline medium are of significance for producing clean fuel to relieve energy and environment crisis.Here,a novel Ni/NiO monolithic electrode was developed by a facile and cost-effective acid promoted activation of Ni foam.After the treatment,this obtained monolithic electrode with a layer of NiO on its surface demonstrates rough and sheet-like morphology,which not only possesses larger accessible surface area but also provides more reactive active sites. Compared with powder catalysts,this monolithic electrode can achieve intimate contact between the electrocatalyst and the current collector,which will alleviate the problem of pulverization and enable the stable function of the electrode. It can be served as an efficient bi-functional electrocatalyst with an overpotential of 160 mV for HER and 290 mV for OER to produce current densities of 10 mA cm^（-2） in the alkaline medium. And it maintains benign stability after 5,000 cycles,which rivals many recent reported noble-metal free catalysts in 1.0mol L^（-1） KOH solution. Attributed to the easy,scalable methodology and high catalytic efficiency,this work not only offers a promising monolithic catalyst but also inspires us to exploit other inexpensive,highly efficient and self-standing noble metalfree electrocatalysts for scale-up electrochemical water-splitting technology.
基金financially supported by the National Natural Science Foundation of China(51903099 and 51991353)Huazhong University of Science and Technology(3004013134 and 2021XXJS036)+1 种基金the 100 Talents Program of the Hubei Provincial Governmentthe Innovation and Talent Recruitment Base of New Energy Chemistry and Device(B21003).
文摘Solar evaporation has emerged as an attractive technology to produce freshwater by utilizing renewable solar energy.However,it remains a huge challenge to develop efficient solar steam generators with good flexibility,low cost and remarkable salt resistance.Herein,we prepare flexible,robust solar membranes by filtration of porous carbon and commercial paper pulp fiber.The porous carbon with well-defined structures is prepared through controlled carbonization of biomass/waste plastics by eutectic salts.We prove the synergistic effect of porous carbon and paper pulp fiber in boosting solar evaporation performance.Firstly,the porous carbon displays a high light absorption,while the paper pulp fiber with good hydrophilicity effectively promotes the transport of water.Secondly,the combination between porous carbon and paper pulp fiber reduces the water vaporization enthalpy by 20%,which is important to significantly improve the evaporation performance.As a proof of concept,the porous carbon/paper pulp fiber membrane possesses a high evaporation rate of 1.8 kg m^(-2)h^(-1)under 1 kW m^(-2)irradiation.Thirdly,the good flexibility and mechanical property of paper pulp fiber enable the solar membrane to work well under extreme conditions(e.g.,after 20 cycles of folding/stretching/recovery).Lastly,due to the super-hydrophilicity and superwetting,the hybrid membrane exhibits the exceptional salt resistance and long-term stability in continuous seawater desalination,e.g.,for 50 h.Importantly,a large-scale solar desalination device for outdoor experiments is developed to produce freshwater.Consequently,this work provides a new insight into developing advanced flexible solar evaporators with superb performance in seawater desalination.
文摘The effect that climatic changes can exert on parasitic interactions represents a multifactor problem whose results are difficult to predict. The actual impact of changes will depend on their magnitude and the physiological tolerance of affected organisms. When the change is considered extreme （i.e. unusual weather events that are at the extremes of the historical distribution for a given area）, the probability of an alteration in an organisms＇ homeostasis increases dramatically. However, factors determining the altered dynamics of host-parasite interactions due to an extreme change are the same as those acting in response to changes of lower magnitude. Only a deep knowledge of these factors will help to produce more accurate predictive models for the effects of extreme changes on parasitic interactions. Extreme environmental conditions may affect pathogens directly when they include free-living stages in their life-cycles and indirectly through reduced resource availability for hosts and thus reduced ability to produce efficient anti-parasite defenses, or by effects on host density affecting transmission dynamics of diseases or the frequency of intraspecific contact. What are the consequences for host-parasite interactions？ Here we summarize the present knowledge on three principal factors in determining host-parasite associations; biodiversity, population density and immunocompetence In addition, we analyzed examples of the effects of environmental alteration of anthropogenic origin on parasitic systems because the effects are analogous to that exerted by an extreme climatic change [Current Zoology 57 （3）： 390405, 2011].
文摘It is difficult to judge whether a given point is a global maximizer of an unconstrained optimization problem. This paper deals with this problem by considering global information via integral and gives a necessary and sufficient condition judging whether a given point is a global maximizer of an unconstrained optimization problem. An algorithm is offered under such a condition and finally two test problems are verified via the offered algorithm.
文摘Extreme weather conditions occur at an increasing rate as evidenced by higher frequency of hurricanes and more extreme precipitation and temperature anomalies. Such extreme environmental conditions will have important implications for all living organisms through greater frequency of reproductive failure and reduced adult survival. We review examples of reproductive failure and reduced survival related to extreme weather conditions. Phenotypic plasticity may not be sufficient to allow adaptation to extreme weather for many animals. Theory predicts reduced reproductive effort as a response to increased stochasticity. We predict that patterns of natural selection will change towards truncation selection as environmental conditions become more extreme. Such changes in patterns of selection may facilitate adaptation to extreme events. However, effects of selection on reproductive effort are difficult to detect. We present a number of predictions for the effects of extreme weather conditions in need of empirical tests. Finally, we suggest a number of empirical reviews that could improve our ability to judge the effects of extreme environmental conditions on life history [Current Zoology 57 （3）： 375-389, 2011].
