By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central ...By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum （SC） in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation （SCG） in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.展开更多
The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight(UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means ...The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight(UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G″) plots at 180 and 200 ℃ versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0.01-100 rad/s for Ziegler-Natta catalyzing ethylene-propylene random copolymerization(PPR) with a conventional molecular weight and broad MWD. The fact indicates that the high molecular weight is responsible for a maximum peak of G″(ω) vs. lnω curves for UHPPH. This makes it possible to determine the plateau modulus(G 0_N) of UHPPH from a certain experimental temperature G″(ω) curve directly. For UHPPH, the G 0_N determined to be 4.28×10 5 and 3.62×10 5 Pa at 180 and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G 0_N has no relation to the molecular weight.展开更多
在压力p=12~32MPa,质量流率G=741~2294 kg/(m^2·s),内壁热负荷q(28)200~870 k W/m^2的参数范围内,以水为工质,对水平倾角25°的倾斜上升光管的传热特性进行了试验研究。试验结果表明:浮力作用是倾斜管传热的重要影响因素。热...在压力p=12~32MPa,质量流率G=741~2294 kg/(m^2·s),内壁热负荷q(28)200~870 k W/m^2的参数范围内,以水为工质,对水平倾角25°的倾斜上升光管的传热特性进行了试验研究。试验结果表明:浮力作用是倾斜管传热的重要影响因素。热负荷对传热具有多重影响。在亚临界压力区,质量流率增量具有界限值,其影响与垂直管中的界限质量流率有所不同。在近临界压力区,增大质量流率或降低热负荷能推迟传热恶化的发生;宏观对流作用可以改善恶化后的传热。在超临界压力区,超临界水的物性变化作用不能减小倾斜管的周向不均匀性。展开更多
基金Project supported by the National Key Basic Research Special Foundation of China(Grant No.2010CB327605 and 2010CB328300)National High-Technology Research and Development Program of China(Grant No.2009AA01Z220)+3 种基金the Key Program of Chinese Ministry of Education(Grant No.109015)the Discipline Co-construction Project of Beijing Municipal Commission of Education(Grant No.YB20081001301)the Open Fund of Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications) of Ministry of Educationthe Specialized Research Fund for the Doctoral Program of Beijing University of Posts and Telecommunications,China(Grant No.CX201023)
文摘By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum （SC） in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation （SCG） in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.
文摘The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight(UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G″) plots at 180 and 200 ℃ versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0.01-100 rad/s for Ziegler-Natta catalyzing ethylene-propylene random copolymerization(PPR) with a conventional molecular weight and broad MWD. The fact indicates that the high molecular weight is responsible for a maximum peak of G″(ω) vs. lnω curves for UHPPH. This makes it possible to determine the plateau modulus(G 0_N) of UHPPH from a certain experimental temperature G″(ω) curve directly. For UHPPH, the G 0_N determined to be 4.28×10 5 and 3.62×10 5 Pa at 180 and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G 0_N has no relation to the molecular weight.
文摘在压力p=12~32MPa,质量流率G=741~2294 kg/(m^2·s),内壁热负荷q(28)200~870 k W/m^2的参数范围内,以水为工质,对水平倾角25°的倾斜上升光管的传热特性进行了试验研究。试验结果表明:浮力作用是倾斜管传热的重要影响因素。热负荷对传热具有多重影响。在亚临界压力区,质量流率增量具有界限值,其影响与垂直管中的界限质量流率有所不同。在近临界压力区,增大质量流率或降低热负荷能推迟传热恶化的发生;宏观对流作用可以改善恶化后的传热。在超临界压力区,超临界水的物性变化作用不能减小倾斜管的周向不均匀性。
