Combustion characteristics in a supersonic combustor with hydrogen injection upstream of cavity flameholder

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of a cavity flameholder were investigated both experimentally and numerically. The combustion was observed to be stabilized in the cavity mode around the shear layer via a dynamic balance and then spread into the main stream in the region around the jet centerplane where the flow was decelerated and turned to the main stream, supplying a favorable condition for the combustion to spread. The combustion spreading from the cavity shear layer to the main stream seemed to be dominated not only by the traditional diffusion process but also by the convection process associated with the extended recirculation flows resulting from the heat release and the interaction between the jet and the cavity shear layer. Therefore, the cavity-stabilized combustion appeared to be a strongly coupled process of flow and heat release around the cavity flameholder.     

EFFECTIVE SPECIFIC HEATS OF SPHERICAL PARTICULATE COMPOSITES WITH INHOMOGENEOUS INTERPHASES

基于细观力学复合球模型研究了含非均匀界面相粒子填充复合材料的有效热弹性性质,重点讨论了界面相性质的径向分布对有效比热的影响. 首先,将非均匀界面相沿径向离散为多个同心球壳,每个球壳内的材料性质假设是均匀的. 基于上述离散模型,利用含界面相的复合球模型,推导了复合材料的有效体积模量、有效热膨胀系数及有效比热的数值求解表达式;进一步,假设界面相的性质沿径向连续变化,建立了一组微分方程,上述有效性质依赖于该微分方程组的解. 特别地,当界面相杨氏模量为幂次分布时,通过求解该微分方程组得到了有效比热等热弹性性质的解析解. 算例结果表明,应用此方法预测的有效热膨胀系数与实验结果吻合良好;界面相热膨胀系数的径向分布对有效比热和有效热膨胀系数均有显著的影响,而界面相弹性模量的径向分布对有效比热有显著的影响,对有效热膨胀系数的影响相对较小.     

低温Yb:YAG放大器增益与热畸变特性实验研究

为了研究低温条件下Yb:YAG放大器的增益和热特性,搭建了一套液氮冷却的低温放大器,开展了实验研究。测量了不同泵浦强度下的小信号增益以及低温和常温下的介质热致波前畸变。结果表明:低温条件下,可以用更少的泵浦能量得到高于常温的增益;常温下泵浦电流200A、脉冲宽度1200μs的小信号增益为1.59;低温下泵浦电流200A、脉冲宽度400μs的小信号增益为1.82,光光效率显著提高。自发辐射放大(ASE)问题在低温下更加显著,采用短脉冲泵浦有利于降低ASE的影响。低温的热管理效果较常温有显著提高,可以在更高的平均功率下运行。     

Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO2 core/shell composite hollow spheres

Anatase TiO₂ shells assembled on hollow glass microspheres (HGM) with tunable morphologies were successfully prepared through a controllable chemical precipitation method with urea as the precipitator. Thus, glass/TiO₂ core/shell composite hollow spheres with low particle density (0.40 g/cm³) were fabricated. The phase structures, morphologies, particle sizes, shell thicknesses, and chemical compositions of the composite microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The morphology of the TiO₂ shell can be tailored by properly monitoring the reaction system component and parameters. The probable growth mechanism and fabrication process of the core/shell products involving the nucleation and oriented growth of TiO₂ nanocrystals on hollow glass microspheres was proposed. A low infrared radiation study revealed that the radiation properties of the products are greatly influenced by the unique product shell structures. A thermal conductivity study showed that the TiO₂/HGM possess low thermal conductivity that is similar to that of the pristine HGMs. This work provides an additional strategy to prepare low-density thermal insulating particles with tailored morphologies and properties.     

A New Phenolate-Ion-Type Two-Photon Near Infrared Fluorophore-Based Biosensor for High-Performance Detection of HNO

Although (E)-4-(2-(4-(dicyanomethylene)-4H-chromen-2-yl)vinyl)phenolate anion (DCPO⁻) has recently emerged as a potential near infrared (NIR) biosensor signaling unit, the pK_a value of its conjugate acid is relatively high (∼9); this will lead to relatively low concentrations of DCPO⁻ under physiological conditions and, hence, unsatisfactory sensitivity of DCPO⁻-based bio-probes. By difluoro-substitution on DCPO⁻, we have exploited a new fluorophore of o-FDCPO⁻ whose conjugate acid has a much lower pK_a value of 7.42. Meanwhile, o-FDCPO⁻ is NIR emissive with λ_em=693 nm and has a 0.76-fold higher fluorescence efficiency than DCPO⁻. The significant superiority of o-FDCPO⁻ over DCPO⁻ in sensitivity for NIR biosensor applications was confirmed by comparative studies on two HNO probes, namely o-FDCPO-P and DCPO-P, which bear signaling units of o-FDCPO⁻ and DCPO⁻, respectively. Moreover, o-FDCPO-P has been demonstrated to be a high-performance HNO probe with high selectivity, high sensitivity (detection limit: 50 nm ), and a rapid response, together with a two-photon NIR-excitation imaging capability.     

Breaking the Passivation: Sodium Borohydride Synthesis by Reacting Hydrated Borax with Aluminum

A significant obstacle in the large-scale applications of sodium borohydride (NaBH₄) for hydrogen storage is its high cost. Herein, we report a new method to synthesize NaBH₄ by ball milling hydrated sodium tetraborate (Na₂B₄O₇ ⋅ 10H₂O) with low-cost Al or Al₈₈Si₁₂, instead of Na, Mg or Ca. An effective strategy is developed to facilitate mass transfer during the reaction by introducing NaH to enable the formation of NaAlO₂ instead of dense Al₂O₃ on Al surface, and by using Si as a milling additive to prevent agglomeration and also break up passivation layers. Another advantage of this process is that hydrogen in Na₂B₄O₇ ⋅ 10H₂O serves as a hydrogen source for NaBH₄ generation. Considering the low cost of the starting materials and simplicity in operation, our studies demonstrate the potential of producing NaBH₄ in a more economical way than the commercial process.     

Amphiphilic Block‐Graft Copolymers Poly(ethylene glycol)‐b‐(polycarbonates‐g‐palmitate) Prepared via the Combination of Ring‐Opening Polymerization and Click Chemistry

Amphiphilic block‐graft copolymers mPEG‐b‐P(DTC‐ADTC‐g‐Pal) were synthesized by ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and 2,2‐bis(azidomethyl)trimethylene carbonate (ADTC) with poly(ethylene glycol) monomethyl ether (mPEG) as an initiator, followed by the click reaction of propargyl palmitate and the pendant azido groups on the polymer chains. Stable micelle solutions of the amphiphilic block‐graft copolymers could be prepared by adding water to a THF solution of the polymer followed by the removal of the organic solvent by dialysis. Dynamic light scattering measurements showed that the micelles had a narrow size distribution. Transmission electron microscopy images displayed that the micelles were in spherical shape. The grafted structure could enhance the interaction of polymer chains with drug molecules and improve the drug‐loading capacity and entrapment efficiency. Further, the amphiphilic block‐graft copolymers mPEG‐b‐P(DTC‐ADTC‐g‐Pal) were low cytotoxic and had more sustained drug release behavior. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Boosting the Quantum Efficiency of Ultralong Organic Phosphorescence up to 52 % via Intramolecular Halogen Bonding

Ultralong organic phosphorescence (UOP) has attracted increasing attention due to its potential applications in optoelectronics, bioelectronics, and security protection. However, achieving UOP with high quantum efficiency (QE) over 20 % is still full of challenges due to intersystem crossing (ISC) and fast non-radiative transitions in organic molecules. Here, we present a novel strategy to enhance the QE of UOP materials by modulating intramolecular halogen bonding via structural isomerism. The QE of CzS2Br reaches up to 52.10 %, which is the highest afterglow efficiency reported so far. The crucial reason for the extraordinary QE is intramolecular halogen bonding, which can not only effectively enhance ISC by promoting spin–orbit coupling, but also greatly confine motions of excited molecules to restrict non-radiative pathways. This work provides a reasonable strategy to develop highly efficient UOP materials for practical applications.     

Existence and regularity of solution of mixed boundary value problem of a Busemann-equation with nonlinear absorb term

The Busemann-equation is a classical equation coming from fluid dynamics. The well-posed problem and regularity of solution of Busemann-equation with nonlinear term are interesting and important. The Busemann-equation is elliptic in y>0 and is degenerate at the line y=0 in R². With a special nonlinear absorb term, we study a nonlinear degenerate elliptic equation with mixed boundary conditions in a piecewise smooth domain. By means of elliptic regularization technique, a delicate prior estimate and compact argument, we show that the solution of mixed boundary value problem of Busemann-equation is smooth in the interior and Lipschitz continuous up to the degenerate boundary on some conditions. The result is better than the result of classical boundary degenerate elliptic equation.     

Simultaneous determination of five aristolochic acids and two aristololactams in Aristolochia plants by high-performance liquid chromatography

An HPLC method was developed for the simultaneous determination of five aristolochic acids (AAs) and two aristololactams (ALs) in the following six Chinese drugs derived from Aristolochia species. Samples were analyzed on a C(18) column with acetonitrile and 3.7 mm phosphoric acid buffer gradient elution, detected at 260 nm. Assay was linear over the range (microg/mL) 0.386-38.6 for aristolochic acid Va, 0.632-63.2 for aristolochic acid IVa, 0.200-20.0 for 9-hydroxy aristolochic acid I, 0.352-35.2 for aristololactam II, 0.296-29.6 for aristolochic acid II, 0.274-27.4 for aristololactam I and 3.12-312 for aristolochic acid I. Average recoveries (%) of samples were 102.0, 95.9, 99.2, 102.2, 97.2, 97.1 and 97.8 for these seven constituents, respectively. The detection limit and retention time for the seven constituents ranged from 10.0 to 15.8 ng/mL and from 12 to 21 min. As a result of drug determination, contents (in mg/g) were as follows: AA-I, 0.69-1.77; AA-II, 0.02-0.18; 9-OH AA-I, 0.04-0.12; AA-IVa, 0.76-3.36; AA-Va, 0.04-0.31; AL-I, 0.07-0.36; and AL-II, 0.01-0.09 in Madouling; AA-I, 0.03-0.41; AA-II, 0.01-0.11; 9-OH AA-I, 0.00-0.60; AA-IVa, 0.00-0.77; AA-Va, 0.00-0.14; and AL-I, 0.00-0.04 in Tianxianteng; AA-I, 1.19-4.71; and AA-II, 0.24-1.69 in Qingmuxiang; AA-I, 2.79-5.48; AA-II, 1.06-1.86; 9-OH AA-I, 0.01-0.09; AA-IVa, 0.38-0.69; AA-Va, 0.00-0.61; AL-I, 0.00-0.02; and AL-II, 0.00-0.02 in Bei-madouling-gen; AA-I, 0.64-4.23; AA-II, 0.06-0.40; and AA-IVa, 0.08-0.25; in Guangfangji; and AA-I, 1.88-9.72; AA-II, 0.26-1.88; and AA-IVa, 0.09-0.52 in Guanmutong. The other constituents were not detected in Tianxianteng, Qingmuxiang, Guangfangji and Guanmutong.