翻白草中鞣质的微波提取工艺研究

采用微波辅助提取方法,以提取剂浓度、pH值、液固比、微波提取时间、温度等为考察因素,并以提取物中总鞣质的提取率为评价指标,使用磷钼钨酸-干酪素分光光度法为定量测定方法,在单因素实验的基础上,通过正交实验优化翻白草中鞣质的提取工艺.实验结果表明,最佳提取条件为:使用70%甲醇作为提取剂、液固比40∶1、提取液pH为8.0、提取温度为40℃、提取时间为10 min.还对翻白草不同部位(根、茎、叶)的鞣质含量进行分析,发现根部中鞣质的含量最大,其次为茎和叶.此外,采用高效液相色谱法对翻白草中鞣质的种类进行定性分析.     

Broad tunability of erbium-doped fiber ring laser based on few-mode polarization maintaining fiber Sagnac interferometer

A highly stable erbium-doped fiber (EDF) ring laser with broad tunability is proposed and experimentally demonstrated. It is accomplished by using a few-mode polarization maintaining fiber (FM-PMF) Sagnac interferometer, in which simultaneous Sagnac and modal interferences occur. Continuously tunable output is obtained by exerting the longitudinal strain on the FM-PMF in combination with adjusting a polarization controller (PC) next to the FM-PMF in the Sagnac interferometer. In addition, the adverse impact of uneven EDF gain distribution on the laser output power uniformity may be offset by the PC-dependent transmission loss of the FM-PMF Sagnac interferometer and reflected backward C-band amplifier spontaneous emission from the pumped EDF. During the whole tuning process, the tunable span covers more than 40 nm with the output power flatness better than 1 dB, 3 dB spectral linewidth narrower than 0.1 nm and optical signal-to-noise extinction ratio higher than 45 dB.     

具有两个不同Ricci主曲率的局部共形平坦Riemann流形

得到了具有常m阶Schouten曲率与两个不同Schouten主曲率(或者等价地,两个不同Ricci主曲率)的完备局部共形平坦Riemann流形的分类结果.作为应用,得到了若干Schouten张量的pinching性质.     

An exact algorithm for the 0–1 linear knapsack problem with a single continuous variable

The 0–1 linear knapsack problem with a single continuous variable (KPC) is an extension of the binary knapsack problem (KP). It is an NP-hard problem. In this paper, we show that KPC can be reduced to KP and a pseudo-knapsack problem (PKP), which is similar to the traditional knapsack problem except that the profits of items may be non-positive, and the weight sum has two sided limits on capacity. We use the Dynamic Programming algorithm COMBO (Martello et al., Manag Sci 45(3):414–424, 1999) to solve KP, and modify the branch and bound method EXPKNAP (Pisinger, Eur J Oper Res 87:175–187, 1995) for KP to solve the PKP. Numerical experiments show the efficiency of our method.     

On hypersurfaces with two distinct principal curvatures in space forms

We investigate the immersed hypersurfaces in space forms ℕ ^n + 1(c), n ≥ 4 with two distinct non-simple principal curvatures without the assumption that the (high order) mean curvature is constant. We prove that any immersed hypersurface in space forms with two distinct non-simple principal curvatures is locally conformal to the Riemannian product of two constant curved manifolds. We also obtain some characterizations for the Clifford hypersurfaces in terms of the trace free part of the second fundamental form.     

Goos-Hänchen shift in bilayer graphene

The quantum Goos-Hänchen (GH) shift of an electron (massive Dirac fermion) at a potential step in bilayer graphene is investigated. We show that the GH shift depends on the step height, the kinetic energy of the electron and incident angle. It is found that the GH shift can be large (positive or negative) under the suitable conditions.     

Contact potential barriers and characterization of Ag-doped composite TiO2 nanotubes

Ag-doping TiO₂ composite nanotubes (Ag-TNTs) were synthesized by alkaline fusion followed by hydrothermal treatment. The microstructure and morphology of the materials were characterized by XRD, TEM, XPS, SPS (surface photovoltage spectroscopy), FISPS (electric field-induced surface photovoltage spectroscopy) and Raman spectroscopy. First-principles calculations based on density-functional theory (DFT) showed the formation of several impurity levels near the top of the valence band in the band gap (E_g) of rutile TiO₂ due to Ag doping. A “double junction” is proposed, involving a Schottky junction and p–n junction (denoted as “Ag-p–n junction”) occurring between the Ag particles and the nanotube surface, as well as forming inside TiO₂ nanotubes, respectively. The strongly built-in electric field of the junctions promotes the separation of photo-holes and photoelectrons, enhancing the photocatalytic efficiency. XRD results indicated that the composite Ag-TNTs exist as a mixture of anatase and rutile phases. XPS results showed that Ti⁴⁺ is the primary state of Ti. Raman spectral analysis of Ag-TNTs revealed the presence of a new peak at 271 cm⁻¹. The red-shift of the absorption light wavelength of Ag-TNTs was 0.16 eV (20 nm) due to a considerable narrowing of E_g by the existing impurity levels.     

Electrochemical effects of isolated voids in uranium dioxide

We present a model to study the electrochemical effects of voids in oxide materials under equilibrium conditions and apply this model to uranium dioxide. Based on thermodynamic arguments, we claim that voids in uranium dioxide must contain oxygen gas at a pressure that we determine via a Kelvin equation in terms of temperature, void radius and the oxygen pressure of the outside gas reservoir in equilibrium with the oxide. The oxygen gas within a void gives rise to ionosorption and the formation of a layer of surface-charge on the void surface, which, in turn, induces an influence zone of space charge into the matrix surrounding the void. Since the space charge is carried in part by atomic defects, it is concluded that, as a part of the thermodynamic equilibrium of oxides containing voids, the off-stoichiometry around the void is different from its remote bulk value. As such, in a uranium dioxide solid with a void ensemble, the average off-stoichiometry level in the material differs from that of the void-free counterpart. The model is applied to isolated voids in off-stoichiometric uranium dioxide for a wide range of temperature and disorder state of the oxide.     

Electronic and optical properties of CdTe under hydrostatic pressure effect

We have determined the pressure dependence of the direct bandgap, ionicity, transverse effective charge and refractive index for CdTe. The study is performed using the sp³s ^* semi-empirical tight-binding method with the scaling law and Murnaghan`s equation of state. All these properties were found to have a sublinearity behaviour with the pressure. The results are compared with other works.     

Magnetic properties of CuSb2−xTaxO6 with tri-rutile structure

We report magnetic properties of CuSb_2−xTa_xO₆ with tri-rutile type structure. Solubility limit was determined to be x=1.0 by the solid-state reaction and X-ray diffraction measurements. The value of J, the magnetic interaction obtained by Bonner–Fisher fitting, was found to decrease gradually with Ta content x. The value of T_N also decreases with x and seems to be zero at x=0.6. As a result of our structural analysis, this fact shows the crossover from one-dimensional to two-dimensional magnetic system with a local distortion caused by Ta substitution. Although the ground state of the compound with x>0.6 is not clear, it can be considered that the long-range antiferromagnetic order disappears and that the quantum critical regime such as a spin-singlet state is realized in this system.