A new cerebroside from fruits of Ailanthus altissima Swingle

A new cerebroside and three known cycloartan triterpenes were isolated from fruits of Ailanthus altissima Swingle. Their structures were identified as 1-O-beta-D-glucopyranosyl-(2S, 3R, 4E, 9E)-2-(2'R-hydroxyhexadecenoy)-4, 9-octadecadiene-1, 3-diol (1), 9, 19-cyclolanost-23 (Z)-ene-3beta, 25-diol (2), cycloart-25-ene-3beta, 24R-diol (3), and cycloart-25-ene-3beta, 24S-diol (4) by means of chemical and spectroscopic analysis. Compounds 2, 3, and 4 were isolated from genus Ailanthus for the first time. The analgesic activity of 1 was also evaluated.     

On the spectral radius of trees with fixed diameter

Let T_{(n, d)} be the set of trees on n vertices with diameter d. In this paper, the first spectral radii of trees in the set T_{(n, d)} (3 ? d ? n − 4) are characterized.     

UV-visible spectroscopic study of the salicyladehyde benzoylhydrazone and its cobalt complexes

Salicyladehyde benzoylhydrazone (SBH) has three groups suitable for forming coordination bond with transition metal. The UV-vis absorption spectra of SBH and its Co(II) complexes in various media were studied by using the deconvolution method. It is found that the structure of complex in solution is different from those in solid crystals. The nature of complexes in solution depends on acidity of the phenolic proton of SBH and on the medium. In neutral or slightly acid medium, the SBH is a non-charged bidentate ligand. And the "free" hydroxyl group on the SBH molecule makes it possible to form hydrogen bonds in solution. In basic medium, the SBH is a mono, negatively charged tridentates ligand.     

The significant digit law in statistical physics

The occurrence of the nonzero leftmost digit, i.e., 1,2,…,9, of numbers from many real world sources is not uniformly distributed as one might naively expect, but instead, the nature favors smaller ones according to a logarithmic distribution, named Benford’s law. We investigate three kinds of widely used physical statistics, i.e., the Boltzmann-Gibbs (BG) distribution, the Fermi-Dirac (FD) distribution, and the Bose-Einstein (BE) distribution, and find that the BG and FD distributions both fluctuate slightly in a periodic manner around Benford’s distribution with respect to the temperature of the system, while the BE distribution conforms to it exactly whatever the temperature is. Thus Benford’s law seems to present a general pattern for physical statistics and might be even more fundamental and profound in nature. Furthermore, various elegant properties of Benford’s law, especially the mantissa distribution of data sets, are discussed.     

Diffusion Tensor Magnetic Resonance Imaging in Ring-Enhancing Cerebral Lesions

The objective of this study is to determine differential diagnostic value of diffusion tensor imaging (DTI) in high-grade brain astrocytomas, brain solitary metastases and brain abscesses. 53 patients with cerebral solitary lesions which showed ring enhancement on contrast-enhanced T ₁-weighted images were enrolled in this study. Brain tissues were examined pathologically from 49 patients to confirm the cerebral occupational diseases. Four patients have been diagnosed with primary cancer plus brain solitary metastasis. DTI measurements were obtained from regions of interest placed on central cavity, white matter of the immediate peritumoral region (IPR) and cerebral white matter of the normal side. The cavity of high-grade astrocytoma and brain metastases displayed hypointense signals; most of the brain abscess cavities displayed high signal intensity except for one case with uneven signal intensity. Mean diffusivity (MD) and fractional anisotropy (FA) values could be used for differentiation between tumor and abscess in brain. The brain abscess cavities showed restricted diffusion and anisotropy [MD = (0.604 ± 0.13) × 10⁻³ mm²/s, FA = 0.185 ± 0.03], whereas the central portion of high-grade astrocytoma [MD = (2.76 ± 0.26) × 10⁻³ mm²/s, FA = 0.069 ± 0.02] and solitary brain metastases [MD = (2.82 ± 0.29) × 10⁻³ mm²/s, FA = 0.064 ± 0.02] showed unrestricted diffusion and isotropy. Brain abscess could be differentiated by MD and FA values in their cavities from brain tumors (P < 0.01). The IPRs were all depicted as hyperintense or isointense signals on diffusion-weighted imaging. The difference between FA values in the IPR of high-grade brain astrocytomas and other groups was statistically significant (P < 0.01). In conclusion, our results suggested the potential role of the cavity MD and FA values in the differential diagnoses of brain tumors and brain abscesses; meanwhile, high-grade astrocytomas could be distinguished from solitary metastases and abscesses by evaluating their corresponding FA values in the IPR on brain magnetic resonance imaging (MRI). Combined with conventional MRI, DTI may help radiologists to facilitate the differential diagnosis of ring-enhancing cerebral lesions in clinical practice.     

Direct fabrication of periodic patterns with hierarchical sub-wavelength structures on poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) thin films using femtosecond laser interference patterning

A simple optical interference method for the fabrication of simply periodic and periodic with a substructure on poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) using femtosecond laser interference patterns is demonstrated. The femtosecond laser pulse was split by a diffractive beam splitter and overlapped with two lenses. Homogeneous periodic arrays could be fabricated even using a single laser pulse. In addition, multipulse irradiation resulted in reproducible sub-wavelength ripples oriented perpendicularly to the laser polarization with spatial period from 170 to 220 nm (around one-fourth of the laser wavelength). In addition, the observed size of the spatial period was not affected by the number of incident laser pulses or accumulated energy density. Using high energy pulses it was possible to completely remove the PEDOT:PSS layer without inducing damage to the underneath substrate.     

Surface modification and characterization of magnesium hydroxide sulfate hydrate nanowhiskers

In order to enhance the compatibility with plastic polymers, magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were modified through grafting methyl methacrylate (MMA) on the surface of the nanowhiskers by emulsion polymerization. The influences of the reaction time, MMA monomer content, adding speed of monomer and the reaction temperature on the grafting ratio were investigated. Thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and surface contact angle measurement were used to characterize the effect of surface modification. The results showed that the MHSH nanowhiskers were uniformly coated by polymethyl methacrylate (PMMA), and a well-defined core-shell hybrid structure of MHSH/PMMA was obtained. The surface contact angle of the hybrid whiskers increased to 87.32° from 12.71° and the whiskers surface was changed from hydrophilic to lipophilic.     

Small AC Driving Voltage for MZI-Based GaAs–GaAlAs Electrooptic Modulators/Switches With Coplanar Electrodes

We report a method to achieve a small ac driving voltage for high-speed multimode interference Mach-Zehnder interferometer GaAs-GaAlAs electrooptic modulators and switches with coplanar electrodes for polarization-insensitive operation. By biasing the devices in the reverse break-down region, the ac driving voltage can be as small as 3 V. Such a small ac driving voltage is important for high-speed optical modulators and switches. The physics behind this small ac driving voltage is also discussed.     

MCMC粒子滤波算法研究及应用

粒子滤波算法是一种基于贝叶斯估计的蒙特卡罗方法,适用于非线性非高斯系统的分析,被广泛应用于跟踪、定位等问题的研究中。为了解决粒子滤波算法在重采样后,丧失粒子多样性的问题,本文在粒子滤波算法的重采样步骤后,加入了马尔可夫链蒙特卡罗（Markov Chain Monte Carlo,简称MCMC）移动步骤,增加粒子的多样性。利用粒子滤波算法和MCMC粒子滤波算法对目标跟踪问题进行了仿真,并且通过分析仿真实验结果,比较了两种算法的性能,结果说明加入MCMC粒子滤波算法的性能优于粒子滤波算法。     

海底光缆研究

自从1985年世界上第一条海底光缆问世以来,海底光缆在全世界得到了广泛发展.海底光缆以其大容量、高可靠性和优异的传输质量等优势,在通信领域,尤其是国际通信中起到了重要的作用.文章简要介绍了海底光缆的技术要求,对海底光缆的典型结构作了分析,概述了海底光缆的关键制造技术和施工程序,并指出了其发展趋势.