Universal power law behavior of the AC conductivity versus frequency of agglomerate morphologies in conductive carbon nanotube‐reinforced epoxy networks

The Jonscher universal power law for ac conductivity versus frequency (f = ω/2π) in the dispersion region was tested for a multiwall carbon nanotube/epoxy nanocomposite. The effect of changes in agglomerate morphology on the fitting parameters A and n in the equation σ_{ac =} Aωⁿ was investigated. Changing nanotube agglomerate morphology was tracked by optical microscopy through curing. Evolving morphology was compared alongside ac conductivity obtained via a broadband dielectric spectrometer to elucidate possible physical meaning of the universal power law in the context of this system. The ?logA/n was unaffected by changes in agglomerate morphology affected during cure, yet connected with each other in their dependence on temperature. For this system, the relationship between the fitting parameters in the universal dynamic response equation remains empirical at this stage with regard to biphasic “texture” or morphology within such a network. Electrical conductivity σ versus frequency ω for a composite consisting of agglomerated multiwalled carbon nanotubes dispersed throughout a cured epoxy matrix was discovered to follow the empirical universal dynamic response equation of Jonscher. The frequency behavior of the exponent n is discussed in terms of underlying morphology throughout which charge carriers migrate. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1918–1923     

NMR‐based analysis of the chemical composition of Japanese persimmon aqueous extracts

Japanese persimmon (Diospyros kaki L.) is recognized as an outstanding source of biologically active compounds relating to many health benefits. In the present study, NMR spectroscopy provided a comprehensive metabolic overview of Japanese persimmon juice. Detailed signal assignments of Japanese persimmon juice were carried out using various 2D NMR techniques incorporated with broadband water suppression enhanced through T₁ effects (BB‐WET) or WET sequences, and 26 components, including minor components, were identified. In addition, most components were quantitatively evaluated by the integration of signals using conventional ¹H NMR and BB‐WET NMR. This is the first detailed analysis combined with quantitative characterization of chemical components using NMR for Japanese persimmon. Copyright © 2015 John Wiley & Sons, Ltd.     

Separating Vibrational Coherences in Ground/Excited Electronic States of Solvent/Solute Following Non-Resonant/Resonant Impulsive Excitation

In a quest to track down the origin of coherent vibrational motions observed in femtosecond pump-probe transients, whether they arise from ground/excited electronic state of solute or are contributed by the solvent, we demonstrate a method for extricating vibrations under resonant and non-resonant impulsive excitations using a diatomic solute in condensed phase (iodine in carbon tetrachloride) with aid of spectral dispersion of the chirped broadband probe. Most importantly, we show how a sum over intensities for a select region of detection wavelengths and Fourier transform of data over select temporal window untwine contributions from vibrational modes of different origins. Thus, in a single pump-probe experiment, vibrational features specific to solute as well as solvent are disentangled that are otherwise spectrally overlapping and are non-separable in conventional (spontaneous/stimulated) Raman spectroscopy employing narrowband excitation. We envision wide-ranging applications of this method to unveil vibrational features in complex molecular systems.     

用于宽谱带发射白色发光二极管的黄色荧光粉Sr8MgAl(PO4)7∶xEu2+的制备及发光性能

通过高温固相反应合成了一系列宽谱带发射黄色荧光粉Sr_8MgAl(PO_4)_7∶x Eu~(2+)(SMAP∶x Eu~(2+)),并对其物质结构、发光性能及其在白色发光二极管(WLED)领域的应用进行了探究。X射线衍射(XRD)测试结果表明,SMAP∶x Eu~(2+)系列荧光粉具有单斜结构和C2/m空间群,激活剂Eu~(2+)离子能够很好地进入SMAP基质中并占据Sr~(2+)离子的晶格位点。漫反射光谱分析显示SMAP基质属于宽带隙材料,带隙宽度为3.60 e V。此外,SMAP∶x Eu~(2+)具有较宽的激发范围(280～500 nm),对应于Eu~(2+)离子的4f~7→4f~65d~1跃迁;在380 nm近紫外光激发下,呈现出450～800 nm的多发光中心的非对称黄光发射,发射峰位于590 nm处。基于高斯多峰拟合结果,得到3个发光中心,分别位于528、600和680 nm。最后,将已制备的黄色荧光粉SMAP∶0.05Eu~(2+)与商业化蓝粉Ba Mg Al_(10)O_(17)∶Eu~(2+)混合涂覆到400 nm芯片上制得色温较好(3 344 K)、显色指数较高(90.1)的WLED。     

Noise and stability in differential delay equations

We study the stability of linear stochastic differential delay equations in the presence of additive or multiplicative white and colored noise. Using a stochastic analog of the second Liapunov method, sufficient conditions for mean square and stochastic stability are derived.     

Analysis of Unsteady Motion with Respect to Noise Sources in a Gas Turbine Combustor: Isothermal Flow Case

In order to evaluate the direct and indirect contributions to the total combustion noise emission, a combustion chamber consisting of a swirl burner and an exit nozzle of Laval-shape, representing a gas turbine combustor, is investigated by means of experiments and large eddy simulation. Focused on the isothermal flow case first and encouraged by a good overall agreement between the LES and the experimental data for the flow field, a first characterisation of the flow with respect to noise sources is performed. To analyse acoustic properties of the flow, time and length scales are evaluated inside the combustor. Furthermore, the evidence for the existence of a precessing vortex core (PVC), typical for configurations with swirl, is revealed. Finally, the effect of the PVC on the flow inside the Laval nozzle is discussed.