利用棱镜谱仪研究氢燃烧转变为爆轰的过程

本文利用Polaroid高速感光底片在一次实验中成功地拍摄到氢燃烧转变为爆轰(DDT)的光谱;利用光电技术研究了氢燃烧转变为爆轰过程中OH基(0.3064μm,0.3428μm)的变化过程.研究表明:在氢燃烧转变为爆轰过程中OH基是逐渐增大的,出现爆轰时OH基出现明显增长;OH(0,0)辐射早于O_2(0,14)辐射,它说明O_2在链式反应中能量比较低,它只有和自由原子和自由基相互碰撞获取高的能量而被激发.     

Unsteady deflagration speed of an auto-ignitive dimethyl-ether (DME)/air mixture at stratified conditions

The propagation speed of an auto-ignitive dimethyl-ether (DME)/air mixture at elevated pressures and subjected to monochromatic temperature oscillations is numerically evaluated in a one-dimensional statistically stationary configuration using fully resolved numerical simulations with reduced kinetics and transport. Two sets of conditions with temperatures within and slightly above the negative temperature coefficient (NTC) regime are simulated to investigate the fundamental aspects of auto-ignition and flame propagation along with the transition from auto-ignitive deflagration to spontaneous propagation regimes under thermal stratification. Contrary to the standard laminar flame speed, the steady propagation speed of an auto-ignitive front is observed to scale proportionally to its level of upstream reactivity. It is shown that this interdependence is primarily influenced by the characteristic residence time and the homogeneous auto-ignition delay. Furthermore, the unsteady reaction front in either of the two cases responds distinctly to the imposed stratification. Specifically, the results in both cases show that the dynamic flame response depends on the mean temperature at the flame base T_b and the time-scale of thermal stratification. It is also found that, based on T_b and the propensity of the mixture to two-stage chemistry, the instantaneous peak propagation speed and the overall time taken to achieve that speed differs considerably. A displacement speed analysis is carried out to elucidate the underlying combustion modes that are responsible for such a variation in flame response.     

不同初始温度下H2/O2混合物等离子体的演化

本文对不同初始温度下,H₂/O₂混合物等离子体中主要粒子随时间发展的演化规律进行了数值模拟,得到了放电后等离子体中主要带电粒子和中性粒子密度随时间的变化规律.计算结果表明,H₂/O₂混合物等离子体中主要活性粒子密度随时间的增加减小,化学反应达到平衡所需的时间随初始温度升高逐渐减少. 关键词： 等离子体 化学过程 数值模拟 演化     

Suppression of indium-composition fluctuations in InGaN epitaxial layers by periodically-pulsed mixture of N_2 and H_2 carrier gas

Indium-composition fluctuations in InGaN epitaxial layers are suppressed by using periodically-pulsed mixture(PPM)of N_2 and H_2 carrier gas. Photoluminescence, optical transmission, reciprocal space map and space-resolved cathodoluminescence are employed to characterize the InGaN epilayers. It is shown that the lateral In-fluctuations mainly occur as hillock-like In-rich regions. Both the number and size of In-rich regions are reduced by introducing the PPM carrier gas.Moreover, the measurements first experimentally demonstrate that the H_2 carrier gas has a stronger decomposition effect on the In-rich region. As the duration time of the PPM carrier gas increases, the reduction of In-content in the In-rich region reaches up to 12%, however, only 2% for the In-homogeneous region. These factors lead to the suppression of In-fluctuations.     

Mode transition in dusty micro-plasma driven by pulsed radio-frequency source in C_2H_2/Ar mixture

Physical qualities of dusty plasma in the pulsed radio-frequency C_2H_2/Ar microdischarges are carefully investigated by a one-dimensional hydrodynamic model and aerosol dynamics model.Since the thermophoretic force has a great effect on the nanoparticle density spatial distribution,the neutral gas energy equation is taken into accounted.The effects of pulse parameters(dust ratio,modulation frequency) on the nanoparticle formation and growth process are mainly discussed.The calculation results show that,as the duty ratio increases,the mode transition from the sheath oscillation(a regime) to the secondary electron heating(7 regime) occurred,which is quite different from the conventional pulsed discharge.Moreover,the effect of modulation frequency on the width of sheath and plasma density is analyzed.Compared with the H_2CC~-ions,the modulation frequency effect on the nanoparticles density becomes more prominent.     

激光激发Cs+H_2系统形成CsH分子机理的实验研究

在Cs-H2混合系统中用激光将Cs原子激发到6P3/2能级,研究了CsH分子的形成机制.利用光学吸收法得到6P3/2态的密度及其空间分布,能量合并过程6P3/2+6P3/2→6D+6S1/2产生6D态原子;猝灭过程Cs(6P3/2)+H2(v=0)→Cs(6S1/2)+H2(v=2)产生H2(v=2)态.由6P3/2态原子密度及6D→6P3/2与6P3/2→6S1/2的荧光比得到碰撞能量合并速率系数,在不同的H2密度下,测量了转移荧光强度I895,得到了H2(2,J)态的产生速率系数kH2(2,J)=1.     

Spectroscopy study of air plasma induced by IR CO2 laser pulses

A spectroscopic study of ambient air plasma, initially at room temperature and pressures ranging from 32 to 101 kPa, produced by high-power transverse excitation atmospheric (TEA) CO₂ laser (λ=9.621 and 10.591 μm; τ _FWHM≈64 ns; power densities ranging from 0.29 to 6.31 GW cm⁻²) has been carried out in an attempt to clarify the processes involved in laser-induced breakdown (LIB) air plasma. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited N, O and ionic fragments N⁺. The medium-weak emission is due to excited species O⁺, N²⁺, O²⁺, C, C⁺, C²⁺, H, Ar and molecular band systems of N ₂⁺(_{2}^{+}( B ²\varSigma _u⁺^{2}\varSigma _{\mathrm{u}}^{+} –X ²\varSigma _g⁺)^{2}\varSigma _{\mathrm{g}}^{+}) , N₂(C³ Π _u–B³ Π _g), N ₂⁺(_{2}^{+}( D² Π _g–A² Π _u) and OH(A² Σ ⁺–X² Π). Excitation temperatures of 23400±700 K and 26600±1400 K were estimated by means of N⁺ and O⁺ ionic lines, respectively. Electron number densities of the order of (0.5–2.4)×10¹⁷ cm⁻³ and (0.6–7.5)×10¹⁷ cm⁻³ were deduced from the Stark broadening of several ionic N⁺ and O⁺ lines, respectively. Estimates of vibrational and rotational temperatures of N ₂⁺_{2}^{+} electronically excited species are reported. The characteristics of the spectral emission intensities from different species have been investigated as functions of the air pressure and laser irradiance. Optical breakdown threshold intensities in air at 10.591 μm have been measured.     

牙齿组织光热动态特性仿真与试验研究

调制激光作用牙齿组织发生散射形成光子密度波, 而由于光热效应产生热波, 基于一维介质辐射传输漫射近似方程与一维热传导方程建立了调制激光作用牙齿组织半透明混合介质的一维热波数学模型. 利用该模型仿真分析了牙齿龋损特性参数(牙釉质龋损层光吸收系数、散射系数、热扩散系数及龋损深度)对光热辐射动态响应特性的影响与规律. 利用红外探测器(HgCdTe, 2–12 μm)记录808 nm半导体激光激发牙齿组织产生的热波信号, 由锁相放大器计算热波信号的幅值与相位. 通过频率扫描试验获得了牙齿组织的光热动态响应, 利用多参数最佳统计拟合方法得到了牙齿组织特性参数. 结果表明光热辐射测量对牙齿组织不均匀性和龋损特性均具有较高敏感性与特异性.     

Initial oxidation of brass induced by humidified air

Complementary surface and near-surface analytical techniques have been used to explore a brass (Cu-20Zn) surface before, during, and after exposure in air at 90% relative humidity. Volta potential variations along the unexposed surface are attributed to variations in surface composition and resulted in an accelerated localized growth of ZnO and a retarded more uniform growth of an amorphous Cu₂O-like oxide. After 3 days the duplex oxide has a total mass of 1.3 μg/cm², with improved corrosion protective properties compared to the oxides grown on pure Cu or Zn. A schematic model for the duplex oxide growth on brass is presented.     

2D computations of FREI with cool flames for n-heptane/air mixture

Two-dimensional axisymmetric numerical simulation reproduced flames with repetitive extinction and ignition (FREI) in a micro flow reactor with a controlled temperature profile with a stoichiometric n-heptane/air mixture, which have been observed in the experiment. The ignition of hot flame occurred from consumption reactions of CO that was remained in the previous cycle of FREI. Between extinction and ignition locations of hot flames, several other heat release rate peaks related to cool and blue flames were observed for the first time. After the extinction of the hot flame, cool flame by the low-temperature oxidation of n-heptane appeared first and was stabilized in a low wall temperature region. In the downstream of the stable cool flame, a blue flame by the consumption reactions of cool flame products of CH₂O and H₂O₂ appeared. After that, the hot flame ignition occurred from the remaining CO in the downstream of the blue flame. Then after the next hot flame ignition, the blue flame was swept away by the propagating hot flame. Soon before the hot flame merged with the stable cool flame, the hot flame propagation was intensified by the cool flame. After the hot flame merged with the stable cool flame, the hot flame reacted with the incoming fresh mixture of n-C₇H₁₆ and O₂.     

热管与蒸气压缩式复合机房空调系统实验研究

搭建了高效利用室外环境空气冷能的分离式热管与蒸气压缩式复合机房空调系统实验台,对系统在热管工况和蒸气压缩式工况的性能进行了实验研究。结果表明:复合空调系统在热管工况下换热量随换热温差、高差、风量的增大而增大;当换热温差进风温差从11.6℃增加到17.4℃,换热量增加了14.4%;风量由2937.4m3/h增加到4196.3m3/h,换热量增加了5.4%;高差由1.1m增大到2.0m,换热量增加了8.3%;该系统的最佳制冷剂充注量为5.4kg。该系统在蒸气压缩式制冷工况下也具有良好的运行效果,且可实现两种模式的灵活切换,表明该复合空调系统是一种的高效可靠机房空调系统。     

用声透射损失测气一水混相介质中的含气量

本文利用超声检测中的穿透法,用频率为０．５ ＭＨｚ、 １ＭＨｚ、 １．２５ＭＨｚ、 ２ＭＨｚ、 ２．５ＭＨｚ的声波,测量了气一水混相介质中的声速比值和声透射损失。结果表明：在气泡大小、分布一定的情况下,可能用声透射损失来确定混相介质中的含气量,但不宜用声速比值．     

用声透射损失测气一水混相介质中的含气量

本文利用超声检测中的穿透法,用频率为０．５ＭＨｚ、１ＭＨｚ、１．２５ＭＨｚ、２ＭＨｚ、２．５ＭＨｚ的声波,测量了气－水混相介质听声速比值和声透射损失,结果表明,在气泡大小,分布一定的情况下,可能用声透射损失来确定混相介质中的含量量,但不宜用声速比值。     

H_2S_2的构型及其异构化的量子化学研究

采用量子化学中的二阶微扰(MP2)方法,在6-311+G(3df,2p)水平上,利用Gaussian软件优化反应物,过渡态和生成物的几何结构,在相同水平上对反应物,过渡态和生成物进行了频率分析,同时完成了内禀反应坐标(IRC)分析.进而利用过渡态理论,计算了温度在300K时的H迁移异构化反应的速率常数.研究结果表明,H2S2的构型有两种,分别为:线型和分叉型,其中线型HSSH的能量较低,为稳定结构;平衡常数很小,为2.2×10-20,不利于平衡从线型向分叉型异构体转化,反之,分叉型向线型转化较容易,因此分     

延迟双脉冲激光产生的空气等离子体的光谱研究

使用激光双光束方法，对激光大气等离子体的光谱进行了实验研究.由一台激光器产生的两束激光，其中一束用于产生等离子体(电离激光束)，另一束则用于对已产生的等离子体施加影响(作用激光束).作用激光束所引起的光谱特征变化的实验研究结果和相应的初步分析.结果表明，在作用激光束的影响下，激光大气等离子体光谱的强度在整体上都有明显的增加，而且，连续光谱的增强大于线状光谱；短波连续光谱的增强大于长波连续光谱；作用激光束相对于电离激光束的延时越大，谱线增强的相对值也越大；作用激光束对谱线的增强不存在明显的阈值效应.结果还表明，作用激光束除导致光谱幅度增强外，对激光大气等离子体中各种类谱线成分的衰变时间也有明显的影响：除个别谱线外，大多数谱线的衰变时间都有不同程度的延长.对结果的初步分析指出，上述结果是激光大气等离子体中的自由电子吸收作用激光束的能量后，在等离子体中有不同传递途径和不同传递效率的体现.该结果为深入了解激光大气等离子体衰变过程中的微观物理现象提供了新的线索，也为以延长激光大气等离子体衰变过程为目标的技术应用提供了实验依据. 关键词： 大气等离子体 双光束 等离子体光谱 谱线演化     

Investigation on the shockwave induced by surface arc plasma in quiescent air

The shockwave induced by surface direct-current （DC） arc discharge is investigated both experimentally and numer- ically. In the experiment, the shockwave generated by rapid gas heating is clearly observed from Schlieren images. The peak velocity of the shockwave is measured to be over 410 m/s; during its upright movement, it gradually falls to about 340 m/s; no remarkable difference is seen after changing the discharge voltage and the pulse frequency. In the modeling of the arc plasma, the arc domain is not simulated as a boundary condition with fixed temperature or pressure, but a source term with a time-varying input power density, which could better reflect the influence of the heating process. It is found that with a reference power density of 2.8× 1012 W/m2, the calculated peak velocity is higher than the measured one, but they quickly （in 30 Its） become agreed with each other. The peak velocity also rises while increasing the power density, the maximum velocity acquired in the simulation is over 468 m/s, which is expected to be effective for high speed flow control.     

飞秒激光空气等离子体发射光谱的实验研究

对强飞秒激光聚焦在空气中所激发的等离子体的发射光谱进行了实验研究.结果表明,光谱特征表现为短波段(截至波长为340 nm)强烈的连续谱和长波段(波长在800 nm附近)强度相对较低的线光谱.在脉冲宽度(50 fs)保持不变而不断调节激光脉冲能量时,等离子体光谱形状的特征基本相似;当激光脉冲能量(1 mJ)保持不变而脉冲宽度从50 fs增加至500 fs和1 ps时,连续谱的峰值(500 nm)显得格外突出,并开始呈现出线光谱特征. 关键词： 飞秒激光 激光空气等离子体 发射光谱 线光谱     

H_2O_2诱导的植物叶片光子辐射的变化及意义

为了研究植物叶片光子辐射与氧化胁迫的关系,将鹅掌木叶片用不同浓度的H_2O_2进行了处理,从而形成氧化胁迫.实验结果表明,随着H_2O_2处理时间的延长,浓度为7.5%、15%和30% 的H_2O_2处理均使鹅掌木叶片光子辐射中的自发发光较未受处理的对照有明显增长,各处理组叶片的延迟发光动力学曲线均呈现双曲性弛豫.通过建立延迟发光非线性动力学方程和数学模拟,得到了延迟发光的特征参量初始光子数I_0、相干时间τ和衰减参量β,发现随着H_2O_2处理时间的延长,各处理组叶片的I_0都呈现先下降,后回升,再下降的波动趋势;而浓度为7.5%和15%的两个处理组的叶片τ值和β值呈现波动变化,浓度为30%的处理组的叶片τ和β呈现单调下降的趋势.推测H_2O_2胁迫下叶片光子辐射中自发发光的变化反映了叶片活性氧含量的变化;叶片延迟发光中I_0的变化反映了细胞总体代谢的变化,延迟发光中的τ值和β值的变化反映了叶片细胞对H_2O_2胁迫的适应和损伤过程.     

飞秒激光成丝过程中由等离子体光栅引起的超连续谱增强与转移

在飞秒宽带激光脉冲成丝过程中, 由于双光束干涉效应而形成的空间等离子体光栅, 研究了空气中飞秒宽带激光脉冲成丝所产生的超连续谱增强效应, 并进一步观测到泵浦光脉冲成丝产生的超连续谱能量向较弱的未成丝的探测光脉冲转移, 有效拓展探测光脉冲带宽的新现象. 通过基于布拉格衍射特性的理论计算较好地解释了实验结果.     

纳秒脉冲激光诱导空气等离子体的近红外辐射特性

开展纳秒激光诱导空气等离子体近红外辐射特性的实验研究,对波长为532 nm的脉冲ns激光诱导产生的空气等离子体的近红外光谱进行测量.结果表明:空气等离子体的近红外辐射在光谱范围为1100-2400 nm内由连续谱和线状谱组成,光谱指认表明线谱主要来源于N,O原子的中性原子谱和氮分子的振动光谱.通过对连续谱的分析得知,黑体辐射是连续辐射的主要来源.空气中波长1128 nm附近的辐射,可能是N和O中性原子谱的贡献.保持真空腔内气压不变,改变腔内氮气和氧气气体组分含量,分析测得的红外光谱数据,可知混合气体中氧气和氮气含量变化只对波长为1128 nm附近的辐射有影响.利用二元线性回归分析对数据进行分析后得知,氧气对波长为1128 nm附近的辐射贡献较大.最后从电离难易的角度分析造成这一结果的原因.