Theoretical analysis of the heat dissipation mechanism in high power photonic crystal fiber lasers

Starting from the special structure of photonic crystal fiber (PCF), the heat dissipation model of a PCF laser is constructed. Based on the heat dissipation model, the temperature distributions along the radial and axial directions of the PCF (DC-Yb-17040) for forward pump of 200 W and two-end pump of 100 W each side are calculated numerically by using the finite element method (FEM). The results show that the temperature distribution for two-end pump mode is more even than that for forward pump mode and the maximum temperature in the fiber decreases by 178.16 °C. With the thermal power in fiber core being assumed to be fixed, the effects of the core radius, outer cladding radius, and air-clad width on the temperature distribution along the fiber are analyzed numerically. The results show that the changing of core radius only affects the temperature in core region slightly and the decreasing of air-clad width decreases the temperature in inner cladding and core regions effectively. Meanwhile, the temperature of the whole fiber can be decreased by increasing the cladding radius.     

Aggregation of quaternary ammonium gemini surfactants C12-s-C12.2Br in n-heptane/n-hexanol solution: effect of the spacer chains on the critical reverse micelle concentrations

The critical reverse micelle concentrations of C(12)-s-C(12).2Br (s=2,3,4,5,6,8,12) in n-heptane/n-hexanol solutions, cmc(I)s, have been determined by absorption spectrum method using iodine as probe. The values of cmc(I)s are smaller than those of the critical micelle concentrations (cmc(aq)s) in aqueous solution and reach a maximum at s=4, which is similar to the variation of cmc(aq) with s. The variation of cmc(I) with s is attributed to the alteration in the spacer chain conformation, i.e. when the spacer is short enough, it may adopt stretch configuration and when the spacer is long, it tends to bend towards the continuous oil phase to achieve a more densely packing of the quaternary ammonium heads on the surface of the core.     

A blow-up criterion for compressible viscous heat-conductive flows

We study an initial boundary value problem for the three-dimensional Navier–Stokes equations of viscous heat-conductive fluids in a bounded smooth domain. We establish a blow-up criterion for the local strong solutions in terms of the temperature and the gradient of velocity only, similar to the Beale–Kato–Majda criterion for ideal incompressible flows.     

Fast preparation of photopolymerized poly(benzyl methacrylate-co-bisphenol A dimethacrylate) monoliths for capillary electrochromatography

A novel porous polymer monolith was prepared in situ in a fused-silica capillary using photoinitiated polymerization. Bisphenol A dimethacrylate (BPADMA) was selected as a crosslinker, copolymerized with benzyl methacrylate (BMA) in the presence of a binary porogenic solvent consisting of cyclohexanol and 1-decanol in ≤10 min. The resulting poly(BMA-co-BPADMA) monoliths exhibited good permeability and mechanical stability. Mixtures of alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs) or phenolic compounds were successfully separated by CEC. A similar monolith was also prepared with ethylene dimethacrylate (EDMA) as the crosslinker instead of BPADMA to compare the separation ability of the resulting monoliths. The results indicated that poly(BMA-co-BPADMA) monoliths have better selectivity for aromatic analytes and greater chromatographic stability in higher aqueous mobile phase.     

Ionic liquid buffers: a new class of chemicals with potential for controlling pH in non-aqueous media

Ionic liquids with buffering characteristics, synthesized by the reaction of [RMIM]OH base moieties with phthalic and tartaric acid, respectively, are potential reagents for controlling pH in non-aqueous media; remarkable [Base]/[Acid] molar ratio dependence of the catalytic activities has been observed in the hydrogenation of olefins with [RuCl2(PPh3)3] complex in DMF and [BMIM][BF4].     

A sugar-quinoline fluorescent chemosensor for selective detection of Hg2+ ion in natural water

A selective and sensitive fluorescent sensor for detection of Hg2+ in natural water was achieved by incorporating the well-known fluorophore quinoline group and a water-soluble D-glucosamine group within one molecule.     

Determination of DL-tetrahydropalmatine in Corydalis yanhusuo by L-tetrahydropalmatine imprinted monolithic column coupling with reversed-phase high performance liquid chromatography

A method for direct determination of DL-tetrahydropalmatine (DL-THP) in Corydalis yanhusuo, a traditional Chinese herb, by L-THP imprinted monolithic precolumn on-line/off-line coupling with reversed-phase high performance liquid chromatography (RP-HPLC) was developed. The L-THP imprinted monolithic column has been prepared by in situ polymerization using methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. With the optimization of chromatographic conditions, such as mobile phase composition, flow rate, column temperature and sample loading, for the separation of enantiomer, DL-THP was base-line separated on the MIP. The imprinted monolithic column was used as a precolumn for fractionation of the C. yanhusuo extract. Both the non-retained and retained fractions were separated by RP-HPLC. Meanwhile, the D-THP and L-THP can be detected in the non-retained and retained fractions, respectively. Additionally, direct determination of L-THP using molecularly imprinted monolith on-line coupling with a reversed-phase column was acquired.     

Fabrication and electrical conductivity of poly(methyl methacrylate) (PMMA)/carbon black (CB) composites: comparison between an ordered carbon black nanowire-like segregated structure and a randomly dispersed carbon black nanostructure

Poly(methyl methacrylate) (PMMA)/carbon black (CB) composites were fabricated using two different mixing methods: (1) mechanical mixing and (2) solution mixing of the precursors, followed by compression molding. The microstructures obtained were examined by optical and scanning electron microscopy. Electrical properties were measured using impedance spectroscopy over a wide frequency range (10(-3) to +10(9) Hz). With the mechanical mixing method, a segregated structure is produced with PMMA particles forming faceted grains with carbon black particles aligning to form a network of 3D-interconnected nanowires. This microstructure allows percolation to occur at a low volume fraction of 0.26 vol % CB. In contrast, specimens made by the solution method have a microstructure where carbon black is distributed more randomly throughout the bulk, and thus, the percolation threshold is higher (2.7 vol % CB). The electrical properties of the PMMA/CB composites fabricated by the mechanical mixing method are comparable to those obtained with single-wall nanotubes as fillers.     

FTIR红外光谱在燃油稀释评价中的应用

为了对柴油车运行过程中发生的燃油稀释润滑油的程度作出及时定量评价,建立了差示红外光谱定量测定润滑油被燃油稀释程度的方法,并根据朗伯-比耳定律建立了吸光度与柴油浓度的校准曲线.结果表明,该分析方法对柴油车使用过程中燃油稀释润滑油的程度能快速准确定量,并且具有重复性好,可信度高的特点.柴油稀释润滑油的程度在0-5.0wt％内呈良好线性关系,线性回归方程为y=0.0085x+0.0048(R2=0.9933).本方法对于发生燃油稀释润滑油的故障能快速诊断,可用于对大批量的行车试验样品进行快速量评估.相对于美国材料与试验协会标准方法ASTM3524中采用气相色谱法来定量分析润滑油中燃油含量,本方法更加快速,使用成本更低廉.