Wide-angle and broadband graded-refractive-index antireflection coatings

The design and fabrication of graded-refractive-index (GRIN) antireflection (AR) coatings with wide-angle and broadband characteristics are demonstrated. The optimization of the graded-index profiles with a genetic algorithm is used in the design of the GRIN AR coatings. The average reflectance over a wavelength range from 400 nm to 800 nm and angles of incidence from 0° to 80° could be reduced to only 0.1% by applying an optimized AR coating onto BK7 glass. The optimization of step-graded GRIN AR coating is then further investigated in detail. A two-layer AR coating was deposited by electron beam evaporation with glancing angle deposition technology, and the positional homogeneity was improved by depositing the film from two opposite directions. The microstructure of the AR coating was investigated by scanning electron microscopy, and the residual reflectances of the coating sample are in agreement with theoretical calculations. The optimized GRIN AR coatings are beneficial to increasing the efficiency of light utilization.     

Structural analysis of unstable norbixin isomers guided by pure shift nuclear magnetic resonance

We report the analysis of complex samples obtained during the microwave irradiation/heating of norbixin, which has been identified as a potential therapeutic target for age-related macular degeneration (AMD). In this context, identifying the different isomers that are obtained during its degradation is of primary importance. However, this characterization is challenging because, on the one hand, some of these isomers are unstable, and on the other hand, the ¹H spectra of these isomeric mixtures are poorly resolved. We could successfully apply 1D pure shift experiments to obtain ultrahigh-resolution ¹H nuclear magnetic resonance (NMR) spectra of the norbixin isomer samples and exploit their information content to analyze complementary 2D NMR data and describe accurately their isomeric composition.     

铒铥共掺氧化锌薄膜近红外宽带发射及变温行为的研究

采用磁控共溅射技术制备了铒铥共掺杂氧化锌发光薄膜. 通过优化退火温度, 实现了薄膜的近红外 平坦宽带发射, 总带宽可达到~ 500 nm, 覆盖了光通信S+C+L+U 区波段. 此发射带由Er³⁺ 的1535 nm (⁴I_13/2 → ⁴I_15/2) 发射峰及Tm³⁺ 的1460 nm (³H₄ → ³F₄), 1640 nm (¹G₄ → ³F₂), 1740 nm (³F₄ → ³H₆) 发射峰组成. 研究表明: 退火温度低于800 ℃ 时, 没有观察到薄膜样品明显的光致发光现象; 随着退火温度 从800 ℃ 升高到1000 ℃, I₁₆₄₀/I₁₅₃₅ 发射峰强度比从0.2 升高到0.3, I₁₇₄₀/I₁₅₃₅ 发射峰强度比从0.5 降低 到0.4, 发射峰强度比均基本保持稳定; 当退火温度高于1000 ℃ 时, I₁₆₄₀/I₁₅₃₅ 发射峰强度比从0.3 升高到 0.6, I₁₇₄₀/I₁₅₃₅ 发射峰强度比从0.4 升高到0.8, 发射峰强度比均急剧增加. 变温行为表明: 随着温度从10 K 逐渐升高到300 K, 谱线的总带宽基本不变, 在340—360 nm 之间; Tm³⁺ 在1640 和1740 nm 处的发射峰强度 分别降低了2/3 和1/2, Er³⁺ 在1535 nm 的发射峰强度增大了1.2 倍. 这是因为随着温度的升高, 声子数目增 多, Er³⁺ 与Tm³⁺ 离子之间发生能量传递的概率不断变大, 并且在Tm³⁺ 离子之间没有发生交叉弛豫现象.     

A rod-airfoil experiment as a benchmark for broadband noise modeling

A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier–Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted in the large anechoic wind tunnel of the Ecole Centrale de Lyon. Measurements taken included particle image velocity (PIV) around the airfoil, single hot wire, wall pressure coherence, and far field pressure. These measurements highlight the strong 3D effects responsible for spectral broadening around the rod vortex shedding frequency in the subcritical regime, and the dominance of the noise generated around the airfoil leading edge. The benchmarking approach is illustrated by two examples:

Structure and stereochemistry of products of hydroxylation of human steroid hormones by a housefly cytochrome P450 (CYP6A1)

The structure and stereochemistry of nine steroid metabolites isolated in quantities ranging from 0.15 to 1.8 mg were determined using a variety of NMR techniques, including heteronuclear multiple bond correlation (HMBC) using broadband adiabatic 13C pulses and phase-sensitive data presentation. Testosterone, androstenedione and progesterone were oxidized with housefly cytochrome P450 6A1 enzyme reconstituted in vitro with housefly NADPH cytochrome P450 reductase and cytochrome b5. NMR analysis in CD3OD using a modified HMBC sequence as well as 2D heteronuclear single quantum correlation (HSQC), COSY and nuclear Overhauser and exchange spectroscopy (NOESY), combined with a detailed analysis of J couplings showed that hydroxylation occurs exclusively on the beta-face of the steroids, at positions 2, 12, and 15.     

A Vector Model of Adiabatic Decoupling

A vector model of adiabatic decoupling is enunciated for an IS-coupled system of two spin- heteronuclei in the high-power limit of ideal adiabatic pulses. The observed S-spin magnetization evolves according to a time-dependent coupling that scales as thezcomponent of an I-spin vector which evolves due to the applied decoupling irradiation. Simple analytical expressions are derived both on and off resonance for the reduced coupling during an ideal sech/tanh inversion pulse and for the resulting signal when either in-phase or antiphase magnetization is present at the start of decoupling. The resulting model allows one to readily envision decoupling experiments, make accurate estimates of sideband intensity, and assess the relative performance of different decoupling schemes. The utility of the model is further demonstrated by applying it to several recently proposed methods for reducing sidebands. In the limit of ideal adiabatic pulses, the predictions of the vector model are almost identical to those of quantum mechanics. At the lower RF power levels used in practical adiabatic decoupling applications, where the pulses are no longer perfectly adiabatic, phase cycles are employed to achieve performance that approximates the ideal limits derived here, so the vector model is more generally applicable, as well. These limits establish standards for future determination of the most efficient parameters for practical applications of broadband adiabatic decoupling in a single transient.     

Application of a 1H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment,using sample spatial encoding and selective echoes

We present the application of a 2D broadband homodecoupled proton NMR experiment to the visualization of enantiomers. In a chiral environment, the existence of diastereoisomeric intermolecular interactions can yield—generally slight—variations of proton chemical shifts from one enantiomer to another. We show that this approach, which relies on a spatial encoding of the NMR sample, is particularly well suited to the analysis of enantiomeric mixtures, since it allows, within one single 2D experiment, to detect subtle chemical shift differences between enantiomers, even in the presence of several couplings. This sequence, which uses semiselective radio‐frequency (rf) pulses combined to a z‐field gradient pulse, produces different selective echoes in various parts of the sample. The resulting homonuclear decoupling provides an original δ‐resolved spectrum along the diagonal of the 2D map where it becomes possible to probe the chiral differentiation process through every proton site where the resulting variation in the chemical shift is detectable. We discuss the advantages and drawbacks of this approach, regarding other experiments which provide homodecoupled proton spectra. This methodology is applied to the observation of enantiomers of (1) ( ± )2‐methyl‐isoborneol coordinated to europium (III) tris[3‐(trifluoromethyl‐hydroxymethylene)‐(+)‐camphorate] in isotropic solution, and (2) ( ± )3‐butyn‐2‐ol dissolved in a chiral liquid‐crystal solvent, in order to show the robustness of this pulse sequence for a wide range of chiral samples. Copyright © 2009 John Wiley & Sons, Ltd.     

多波长宽带拉曼放大器的优化设计

简化多波长宽带拉曼放大器功率耦合方程,利用多步平均功率法进行数值计算得到密集波分复用系统信号的合成拉曼增益.对传统的模拟退火优化算法进行改进,并应用于宽带拉曼放大器增益谱的优化设计.提出新的目标函数,综合考虑增益带宽、开关增益、增益平坦度等特征参数.基于该简化模型和优化方法研究多泵浦光源的个数、输入功率和波长分布对信号拉曼增益的影响,揭示拉曼放大器增益带宽、开关增益、增益平坦度、泵浦数目等主要参数之间的内在联系.仿真结果显示,信号平坦增益带宽△λ随着泵浦数的增多显著加宽,随开关增益的提高和平坦度的增加明显变窄.     

冻土纵,横波复合宽带超声换能器系列研制

根据冻土弹性波测试的要求,本文研制成功一种冻土测试用２５０ｋＨｚ、５００ｋＨｚ和１ＭＨｚ系列的纵波、横波复合宽带超声换能器。这种换能器具有灵敏度高、频带宽、声阻抗低的特点,适于冻土力学特性测试。作者介绍了它的结构及相应系统特性,并以１０ｐｓ的延时间精度,在零度以下气温条件下,实测了不同含水量（７％、１０％、１６％、２２％和２５％）及负温（－２℃、－４０℃、－６℃、－８℃、－１０℃、－１２℃、－１４     

光纤同轴电缆混合网技术

阐述了光纤同轴电缆混合网 (HFC)网络的主要工作原理 ,给出了 HFC网络的基本结构模型 .对 HFC网络媒体存取控制 (MAC)层中的 3个重要问题 ,即上行通道访问模式、同步问题、碰撞解决方案及其解决方案进行了讨论 ,并对 HFC技术中存在的噪声干扰问题以及解决办法进行了初步的探讨 .