Preconcentration sensitive determination of pyrethroid insecticides in environmental water samples with solid phase extraction with SiO2 microspheres cartridge prior to high performance liquid chromatography

Present study developed a new method for the sensitive determination of pyrethroid insecticides with solid phase extraction in combination with high performance liquid chromatography and UV detector. SiO₂ microspheres, a new SiO₂ based material, was investigated for the enrichment ability and applicability as the solid phase extraction sorbent. Four pyrethroid pesticides such as fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were used as the target analytes. Parameters that maybe influence the extraction efficiency such as the eluent type and its volume, sample flow rate, sample pH, and the sample volume were optimized in detail, and the optimal conditions were as followed: sample volume, 100 mL; concentration of methanol, 30%; acetone volume, 5 mL; sample flow rate, 4.2 mL min⁻¹; sample pH, 7. The experimental results indicated that there was good linearity in the concentration range of 0.1–50 μg L⁻¹ except biphenthrin in the range of 0.05–25 μg L⁻¹. The detection limits for fenpropathrin, cyhalothrin, fenvalevate and biphenthrin were in the range of 0.02–0.08 μg L⁻¹. The intra-day and day to day precisions (RSDs, n = 6) were in the ranges of 2.6–4.4% and 5.3–7.2%, respectively. The method was validated with five real environmental water samples, and all these results proved that proposed method could be used as a good alternative for the routine analysis for such pollutants in environmental samples.     

Composition determination of binary polymer mixtures by size exclusion chromatography with light scattering detection

<正>Base on the principle of absolute quantification of size exclusion chromatography(SEC),a light scattering(LS) detector coupled with a concentration detector(refractive index detector) is utilized to determine the compositions of complicated binary mixtures.A theoretical analysis predicts that the response factors for both LS and RI detectors are linear functions with the composition of any specified polymer mixtures in the binary polymer mixtures.Two pairs of complicated binary mixtures were used to test the theory mentioned in the present paper,and the experimental results show an excellent accordance with the theory.     

RAFT聚合合成一种即含甲酰基又含手性β-蒎烯单元聚合物

设计并合成了一种新型含甲酰基同时又含β-蒎烯单元的新单体2-β-蒎氧基-5-乙烯基苯甲醛(POVB),选择苯基双硫代乙酸1-苯基乙酯(PEPDA)为RAFT试剂、以AIBN为引发剂、在60℃下THF中实现了POVB的"活性"/可控RAFT自由基聚合.单体浓度半对数ln([M]0/[M])与聚合时间符合线性关系,聚合过程呈现一级动力学特征;聚合物分子量(Mn)随单体转化率几乎线性增加,而且整个反应过程中分子量分布(Mw/Mn1.2)保持在较窄的范围.1H-NMR的分析进一步证实了聚合物链的末端精细结构.此外,CD谱结果表明手性单元β-蒎烯基能赋予聚合物以光学活性.     

黄孢原毛平革菌210对稀土离子的吸附作用研究

通过电感耦合等离子体发射光谱(ICP-OES)、扫描电镜等手段研究了黄孢原毛平革菌210对镧离子(La3+)及其他稀土离子的吸附能力。结果表明,在pH=7,La3+浓度为40 mg.L-1,菌体投加量60 mg.L-1(以干重计),吸附时间120 min时,黄孢原毛平革菌210的吸附量最大,达141.5±4.72 mg.g-1。经盐酸预处理的菌体吸附能力有所提高,其他预处理则使菌体吸附能力下降。解吸剂柠檬酸和EDTA都能较好地解吸La3+。黄孢原毛平革菌210对单一稀土离子的吸附能力差异较大。在15种混合稀土离子溶液中,对Lu3+,Sm3+,Eu3+的吸附量较高,对混合稀土离子具有一定的富集、分离作用。扫描电镜发现La3+可能主要以盐的形式沉积在菌体表面上。     

GHz microwave properties of melt spun Fe-Si alloys

The structural and microwave properties of melt spun Fe_100−xSi_x (x = 10, 20, 30) nanocomposites were investigated. The phases varied with Si content in FeSi alloys. It is found that the Fe₃Si and FeSi phases could be obtained with Si content up to 20 at.%. The X-ray absorption fine structure (XAFS) spectra of Fe K-edges show that the local structures around Fe atoms in melt spun Fe-Si alloys become more disordered with increasing Si content when compared with that of α-Fe. The complex permittivity-frequency and permeability-frequency properties were determined in the microwave frequency regime of 2-18 GHz by vector network analysis. It is found that flake-like FeSi powder composite has the largest values of μ′ and μ″ at 2 GHz. The reflection loss shifts to the higher frequency with the Si content increasing for melt spun FeSi alloys. A minimum reflection loss of −16.5 dB is obtained at 13.9 GHz for composition Fe₇₀Si₃₀ with the thickness of 1.5 mm. However, for composition Fe₇₀Si₃₀, the minimum reflection loss shifts to lower frequency and larger value with the thickness increasing. The results suggest a new design for microwave absorbers based on electromagnetic wave-absorbing materials.     

光电子成像研究AgOCH3-和Ag-(CH3OH)x (x=1, 2)

用光电子成像技术和从头算法研究Ag^-(CH₃OH)_x (x=1, 2)和AgOCH₃^-. 从AgOCH₃^-振动分辨的光电子谱得 到AgOCH₃^-的绝热和垂直电离能分别为1.29(2)和1.34(2) eV. Ag^-(CH₃OH)_{1,2相似文献}   

Burst synchronization transitions in a neuronal network of subnetworks

In this paper, the transitions of burst synchronization are explored in a neuronal network consisting of subnetworks. The studied network is composed of electrically coupled bursting Hindmarsh-Rose neurons. Numerical results show that two types of burst synchronization transitions can be induced not only by the variations of intra- and intercoupling strengths but also by changing the probability of random links between different subnetworks and the number of subnetworks. Furthermore, we find that the underlying mechanisms for these two bursting synchronization transitions are different: one is due to the change of spike numbers per burst, while the other is caused by the change of the bursting type. Considering that changes in the coupling strengths and neuronal connections are closely interlaced with brain plasticity, the presented results could have important implications for the role of the brain plasticity in some functional behavior that are associated with synchronization.     

Projective synchronization of two coupled excitable spiral waves

Interaction of two identical excitable spiral waves in a bilayer system is studied. We find that the two spiral waves can be completely synchronized if the coupling strength is sufficiently large. Prior to the complete synchronization, we find a new type of weak synchronization between the two coupled systems, i.e., the spiral wave of the driven system has the same geometric shape as the spiral wave of the driving system but with a much lower amplitude. This general behavior, called projective synchronization of two spiral waves, is similar to projective synchronization of two coupled nonlinear oscillators, which has been extensively studied before. The underlying mechanism is uncovered by the study of pulse collision in one-dimensional systems.     

Positive solutions of the system for nth-order singular nonlocal boundary value problems

The paper deals with the existence and multiplicity of positive solutions to systems of nth-order singular nonlocal boundary value problems. The main tool used in the proof is fixed point index theory in cone. Some limit type conditions for ensuring the existence of positive solutions are given.     

Study of acoustic field modulation in the regenerator by double loudspeakers method

A model to modulate acoustic field in a regenerator of a thermoacoustic system by the double loudspeakers method is presented in this paper. The equations are derived for acoustic field modulation. They represent the relations among acoustic field (complex pressure p(0), complex velocity u(0), and acoustic impedance Z(0)), driving parameters of loudspeakers (voltage amplitude and its phase difference), and operating parameters involved in a matrix H (frequency, temperature of regenerator). The range of acoustic field is adjustable and limited by the maximal driving voltages of loudspeakers according to driving parameters. The range is simulated and analyzed in the amplitude-phase and complex coordinate planes for a given or variable H. The simulated results indicate that the range has its intrinsic characteristics. The expected acoustic field in a regenerator can be obtained feasibly by the modulation.