An improved fishnet three-dimensional metamaterial with multiband left-handed characteristics at terahertz frequencies

We present the design of a multiband left-handed three-dimensional (3D) metamaterial based on improved fishnet structure at terahertz frequencies. The design realizes a three-dimensional material by mechanical stacking of multiple layers. The electromagnetic properties of the metamaterial have been investigated by numerical simulation. The results show that simultaneously negative values of permittivity, permeability and refractive index are found around the frequencies of 0.73, 0.85 and 1.12 THz for the electromagnetic wave normal incidence. The proposed metamaterial with independent polarization and compact effect offers a way to develop THz 3D materials and devices suitable for multifrequencies.     

谱图检索结合二级质谱定性分析烟草中挥发性成分

采用同时蒸馏萃取法提取烟叶中的挥发性成分,利用气相色谱-质谱联用仪(GC-MS)分离测定,通过谱库检索和匹配度定性结合色谱保留指数方法鉴定烟叶中挥发性成分,并引入离子阱二级质谱对谱库检索匹配度差距小、含量低,背景干扰大的物质准确定性.采用谱图检索结合二级质谱定性共鉴定144个化合物,其中104个化合物在烟草挥发性成分的文献中已有报道,报道中有9个化合物是通过二级质谱定性,其余40个化合物还未见报道.结果表明,离子阱二级质谱定性的引入提高了对未知化合物定性的准确性和可靠性,适合于烟叶这类复杂植物体系的化学组分研究.     

Thermal runaway features of 18650 lithium-ion batteries for LiFePO4 cathode material by DSC and VSP2

In view of availability, accountability, and applicability, LiFePO₄ cathode material has been confirmed to be better than LiCoO₂ cathode material. Nevertheless, few related researches were conducted for thermal runaway reaction of the LiFePO₄ batteries. In this study, vent sizing package 2 (VSP2) and differential scanning calorimetry were employed to observe the thermal hazard of 18650 lithium-ion batteries and their content??LiFePO₄ cathode material, which were manufactured by Commercial Battery, Inc. Two states of the batteries were investigated, which was charged to 3.6?V (fully charged) and 4.2?V (overcharged), respectively, and important parameters were obtained, such as self-heating rate (dT?dt ^?1), pressure-rise rate (dP?dt ^?1), and exothermic onset temperature (T ₀). The results showed that T ₀ for fully charged is about 199.94?°C and T _max is about 243.23?°C. The entire battery for LiFePO₄ cathode material is more stable than other lithium-ion batteries, and an entire battery is more dangerous than a single cathode material. For process loss prevention, the data of battery of VSP2 test were applied as reference for design of safer devices.     

Two novel abietane norditerpenoids with anti-inflammatory properties from the roots of Salvia miltiorrhiza var. alba

Salvialba acid (1) with a novel abietane norditerpenoid skeleton and 2-hydroxydihydrotanshinone I (2), a new abietane norditerpenoid, were isolated from Salvia miltiorrhiza var. alba. Their structures were elucidated by spectroscopic analysis and X-ray diffraction. The absolute configuration of 1 was determined by an electronic circular dichroism (ECD) experiment and TDDFT ECD computations. A possible biosynthesis pathway is proposed for 1. Compounds 1 and 2 were demonstrated to have anti-inflammatory effects on vascular inflammation induced by TNF-α in human aortic endothelial cells (HAECs).     

胡蜂蜂毒肽的固相合成

采用Fmoc固相合成策略,合成了胡蜂蜂毒肽(COOH-Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH₂)。以Wang树脂为载体,HBTU-HOBt为缩合剂,按照其氨基酸序列依次缩合,最终用切割试剂将其从树脂上切割下来,得到粗肽,经RP-HPLC纯化得到目标肽,纯度97.6%。经HR-MS（EI）分析,确定产物为胡蜂蜂毒肽。     

Structural characteristics and spectral behaviours of the preferred conformation of a cyclic pentapeptide,cycloaspeptide G from Cordyceps-colonising fungus Isoria farinose

The density functional theory (DFT) is exploited to search the stable conformations of a cyclic pentapeptide called cycloaspeptide G from Cordyceps-colonising fungus Isoria farinose. Its time-dependent version is employed to describe the profiles of electronic circular dichroism (ECD) of the preferred conformation, where the solvent effect in methanol is taken into account on the basis of the polarisable continuum model computation. Four stable conformers are optimised, and the results of the harmonically vibrational frequency calculations illustrate that they are the true minima. In the vibrational CD spectrum at the B3LYP/6-31G* level, the negative peak at 3334 cm^?1 has its origin of the NH stretches of the peptide ring. In the ECD spectrum at the B3LYP/6-31G* level, three strong bands are negative, positive, and negative. Since the ECD spectrum at the B3LYP/6-31G* level is remarkably different from that at the B3LYP/6-31G level, it is necessary for the expended functions to be added to the 6-31G basis set.     

Synthesis and properties of (−)-menthol-derived chiral liquid crystals by introducing adipoyloxy spacer between mesogenic core and chiral menthyl

A homologous series of new chiral liquid crystal compounds, M6BnB (n = 2, 4, 6, 8, 10, 12, 14, 16, 18), with varying length of n-alkoxy chains at one end, was formed by covalently linking a chiral (?)-menthyl with biphenyl-benzoate via adipoyloxy spacer group. A combination of analysis methods such as Fourier transform infrared, ¹H NMR spectra, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length of the flexible terminal alkoxy group has a profound influence on the clearing points (T_iso) and T_iso decrease with the increase of alkoxy chain (n). In addition, increasing the length of the terminal alkoxy group tends to narrow the temperature range of the N* phase and favour the development of chiral smectic C phase.     

Stability and Hopf bifurcation for a three-component reaction–diffusion population model with delay effect

A delayed three-component reaction–diffusion population model with Dirichlet boundary condition is investigated. The existence and stability of the positive spatially nonhomogeneous steady state solution are obtained via the implicit function theorem. Moreover, taking delay τ$\tau$ as the bifurcation parameter, Hopf bifurcation near the steady state solution is proved to occur at the critical value _τ0${\tau }_0$. The direction of Hopf bifurcation is forward. In particular, by using the normal form theory and the center manifold reduction for partial functional differential equations, the stability of bifurcating periodic solutions occurring through Hopf bifurcations is investigated. It is demonstrated that the bifurcating periodic solution occurring at _τ0${\tau }_0$ is orbitally asymptotically stable. Finally, the general results are applied to four types of three species population models. Numerical simulations are presented to illustrate our theoretical results.