Purpose： The purpose of this review was to critically analyse the cun;ent evidence investigating the effect of an athlete＇s hydration status on physical performance. Methods： A literature search of multiple databas...Purpose： The purpose of this review was to critically analyse the cun;ent evidence investigating the effect of an athlete＇s hydration status on physical performance. Methods： A literature search of multiple databases was used to identify studies that met the inclusion criteria for this review. The included studies were then critically appraised using the Downs and Black protocol. Results： Nine articles were found to meet the inclusion criteria, with an average score of 79% for methodological quality representative of a ＂high＂ standard of research. Conclusion： The evidence suggests that dehydration has a negative impact on physical performance for activities lasting more than 30 s in duration. However dehydration was found to have no significant impact on physical performance for activities lasting less than 15 s in duration.展开更多
With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of op...With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of optical fiber connectors were investigated. The return loss of optical fiber connectors is 32CD*238dB before polishing. The results show that dry polishing（i.e. no polishing fluid） with Al2O3 has less influence on return loss of optical fiber connectors, while dry polishing with SiO2 reduces return loss to about 20dB because of the end-face of optical fiber contaminated. The wet polishing（i.e. using distilled water as polishing fluid） with Al2O3 or SiO2 can increase return loss to 45CD*250dB, but wet polishing with Al2O3 may produce optical fiber undercut depth of 80CD*2140nm. Wet polishing with SiO2 should be preferentially selected for optical fiber connectors and polishing time should be controlled within 20CD*230s.展开更多
Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive wer...Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.展开更多
The studied sample is a metallic glass in Fe-Si-B system. It is developed with the nominal composition of Fe735-Cu1-Ta3-Si13.5-B9 by single-roller melt spinning technique in air. The dielectric constant and loss facto...The studied sample is a metallic glass in Fe-Si-B system. It is developed with the nominal composition of Fe735-Cu1-Ta3-Si13.5-B9 by single-roller melt spinning technique in air. The dielectric constant and loss factor have been measured both for as cast and annealed samples using Agilent Impedance analyzer. They are found to decrease with frequency up to 10 MHz and remain constant afterwards. The decrease of dielectric constant and loss factor with frequency is due to ceasing of orientational polarizability. Their constancy is owing to presence of only electronic contribution to its polarizability above 10 MHz. Three distinct regions （1-4 MHz, 4-10 MHz and 10 MHz-1 GHz） also noticed from its frequency dependence, which might make it useful in switching and sensor devices. The temperature dependence of dielectric constant and loss factor maintain inverse relationship： （1） dielectric constant increases, and （2） loss factor decreases with annealing temperature for structural relaxation due to thermal agitation.展开更多
The electrical, physical, mechanical and thermal properties of fluorine-containing alicyclic polyimides have been investigated. It was shown that the minimum value of the dielectric constant 1.91 at room temperature a...The electrical, physical, mechanical and thermal properties of fluorine-containing alicyclic polyimides have been investigated. It was shown that the minimum value of the dielectric constant 1.91 at room temperature and 1 kHz frequency was achieved for polymers containing only one fluorine atom in the structure. The dielectric loss tangent of new polymers was （I -4）~ 103. Electro-physical parameters were stable during polymer heating up to 300 ~C, and at the frequency from 1 to 20 kHz. Resistivity by heating in the air up to 320-380 ~C has been investigated depending on the polyimides structure. The coefficient of moisture absorption for the fluorine-containing polyimide based on dianhydride with 4,4＇-oxydianiline was determined at 50% humidity and 25 ℃. It was around 0.6, but after immersion in the water for 24 and 48 h was 0.8% and 1.2%, respectively. Manufactured films had tensile strength to 160-170 MPa, and elongation up to 55%.展开更多
We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza- tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 ce...We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza- tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 cells with different capacities and electrode materials are evalu- ated by measuring input and output energy which change with charge-discharge time and current. Based on the results of these tests, we build a model of energy loss in cells＇ charge- discharge process, which include Joule heat and polarization heat impact factors. It was reported that Joule heat was caused by cell resistance, which included De-resistance and reaction resistance, and reaction resistance could not be easily obtained through routine test method. Using this new method, we can get the total resistance R and the polarization parameter U. The relationship between R, η, and temperature is also investigated in order to build a general model for series of different Li-ion batteries, and the research can be used in the performance evaluation, state of charge prediction and the measuring of consistency of the batteries.展开更多
随着接入网和FTTH不断发展，对于光纤也提出新的要求，这时候传统的、大量使用的G．652光纤在某些场合已经不能完全满足使用需求，所以在2006年的12月，ITU推出了新的G．657弯曲损耗不敏感单模光纤（bending loss insensitive single mo...随着接入网和FTTH不断发展，对于光纤也提出新的要求，这时候传统的、大量使用的G．652光纤在某些场合已经不能完全满足使用需求，所以在2006年的12月，ITU推出了新的G．657弯曲损耗不敏感单模光纤（bending loss insensitive single mode optical fiber）的标准，G．657光纤分为G．65VA和G．657B两类。G．657A需与常规的G．652D光纤完全兼容，弯曲半径可以小到10mm；展开更多
Mg-doped CaCu_(3-x)Mg_(x)Ti_(4)O_(12)(x=0,0.05,0.1,0.15,0.2,at.%)thin films were prepared by a modified sol−gel method.A comparative study on the microstructure and electrical properties of Mg-doped CaCu_(3)Ti_(4)O_(1...Mg-doped CaCu_(3-x)Mg_(x)Ti_(4)O_(12)(x=0,0.05,0.1,0.15,0.2,at.%)thin films were prepared by a modified sol−gel method.A comparative study on the microstructure and electrical properties of Mg-doped CaCu_(3)Ti_(4)O_(12)(CCTO)thin films was carried out.The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films.Furthermore,compared to undoped CCTO films,Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability.Meanwhile,Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 104−106 Hz.The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films.The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0,respectively.展开更多
文摘Purpose： The purpose of this review was to critically analyse the cun;ent evidence investigating the effect of an athlete＇s hydration status on physical performance. Methods： A literature search of multiple databases was used to identify studies that met the inclusion criteria for this review. The included studies were then critically appraised using the Downs and Black protocol. Results： Nine articles were found to meet the inclusion criteria, with an average score of 79% for methodological quality representative of a ＂high＂ standard of research. Conclusion： The evidence suggests that dehydration has a negative impact on physical performance for activities lasting more than 30 s in duration. However dehydration was found to have no significant impact on physical performance for activities lasting less than 15 s in duration.
文摘With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of optical fiber connectors were investigated. The return loss of optical fiber connectors is 32CD*238dB before polishing. The results show that dry polishing（i.e. no polishing fluid） with Al2O3 has less influence on return loss of optical fiber connectors, while dry polishing with SiO2 reduces return loss to about 20dB because of the end-face of optical fiber contaminated. The wet polishing（i.e. using distilled water as polishing fluid） with Al2O3 or SiO2 can increase return loss to 45CD*250dB, but wet polishing with Al2O3 may produce optical fiber undercut depth of 80CD*2140nm. Wet polishing with SiO2 should be preferentially selected for optical fiber connectors and polishing time should be controlled within 20CD*230s.
基金Project(50872052) supported by the National Natural Science Foundation of ChinaProject(2009AA05Z313) supported by the National High Technology Research and Development Program of ChinaProject supported by the Commission of Science,Technology and Industry for National Defence,China
文摘Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.
文摘The studied sample is a metallic glass in Fe-Si-B system. It is developed with the nominal composition of Fe735-Cu1-Ta3-Si13.5-B9 by single-roller melt spinning technique in air. The dielectric constant and loss factor have been measured both for as cast and annealed samples using Agilent Impedance analyzer. They are found to decrease with frequency up to 10 MHz and remain constant afterwards. The decrease of dielectric constant and loss factor with frequency is due to ceasing of orientational polarizability. Their constancy is owing to presence of only electronic contribution to its polarizability above 10 MHz. Three distinct regions （1-4 MHz, 4-10 MHz and 10 MHz-1 GHz） also noticed from its frequency dependence, which might make it useful in switching and sensor devices. The temperature dependence of dielectric constant and loss factor maintain inverse relationship： （1） dielectric constant increases, and （2） loss factor decreases with annealing temperature for structural relaxation due to thermal agitation.
文摘The electrical, physical, mechanical and thermal properties of fluorine-containing alicyclic polyimides have been investigated. It was shown that the minimum value of the dielectric constant 1.91 at room temperature and 1 kHz frequency was achieved for polymers containing only one fluorine atom in the structure. The dielectric loss tangent of new polymers was （I -4）~ 103. Electro-physical parameters were stable during polymer heating up to 300 ~C, and at the frequency from 1 to 20 kHz. Resistivity by heating in the air up to 320-380 ~C has been investigated depending on the polyimides structure. The coefficient of moisture absorption for the fluorine-containing polyimide based on dianhydride with 4,4＇-oxydianiline was determined at 50% humidity and 25 ℃. It was around 0.6, but after immersion in the water for 24 and 48 h was 0.8% and 1.2%, respectively. Manufactured films had tensile strength to 160-170 MPa, and elongation up to 55%.
文摘We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza- tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 cells with different capacities and electrode materials are evalu- ated by measuring input and output energy which change with charge-discharge time and current. Based on the results of these tests, we build a model of energy loss in cells＇ charge- discharge process, which include Joule heat and polarization heat impact factors. It was reported that Joule heat was caused by cell resistance, which included De-resistance and reaction resistance, and reaction resistance could not be easily obtained through routine test method. Using this new method, we can get the total resistance R and the polarization parameter U. The relationship between R, η, and temperature is also investigated in order to build a general model for series of different Li-ion batteries, and the research can be used in the performance evaluation, state of charge prediction and the measuring of consistency of the batteries.
文摘随着接入网和FTTH不断发展，对于光纤也提出新的要求，这时候传统的、大量使用的G．652光纤在某些场合已经不能完全满足使用需求，所以在2006年的12月，ITU推出了新的G．657弯曲损耗不敏感单模光纤（bending loss insensitive single mode optical fiber）的标准，G．657光纤分为G．65VA和G．657B两类。G．657A需与常规的G．652D光纤完全兼容，弯曲半径可以小到10mm；
基金the financial supports from the National Natural Science Foundation of China(Nos.52072004,51802003,51572113)。
文摘Mg-doped CaCu_(3-x)Mg_(x)Ti_(4)O_(12)(x=0,0.05,0.1,0.15,0.2,at.%)thin films were prepared by a modified sol−gel method.A comparative study on the microstructure and electrical properties of Mg-doped CaCu_(3)Ti_(4)O_(12)(CCTO)thin films was carried out.The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films.Furthermore,compared to undoped CCTO films,Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability.Meanwhile,Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 104−106 Hz.The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films.The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0,respectively.
