The application of chemical reduction methods to a combustion system exhibiting complex dynamics

A number of chemical model reduction techniques have been developed over recent years with a growing range of applications in combustion. The following work demonstrates the application of such reduction techniques for a combustion system describing the oxidation of carbon monoxide + hydrogen in a continuously stirred tank reactor (CSTR) at very low pressure. The system exhibits complex dynamics including oscillatory glow, oscillatory ignition and mixed mode oscillations. It is demonstrated that a range of local reduction methods can be applied to such complex systems, as long as sufficient coverage of the accessed regions of phase space are included in the reduction analysis. The methods include sensitivity analysis, the quasi-steady state approximation (QSSA) and repro-modelling based on the concept of an intrinsic low dimensional manifold (ILDM). The system is qualitatively different from some previous applications of ILDM methods where trajectories tend towards a fixed equilibrium. The underlying dimension of the system is seen to vary throughout selected trajectories with rapid increases occurring over very short time-scales during oscillatory ignition. Nevertheless, a final reduced model of only four variables is developed using fitted orthonormal polynomials describing the system dynamics on a slow manifold. The application serves to demonstrate that the relationship between local reduced model error and global errors can be complex for systems exhibiting complex dynamics, with regions of seemingly small local mapping gradients requiring tighter error control in order to control global errors. This feature may be common in cases where nearby trajectories are seen to diverge within the slow manifold over time.     

A detailed chemical kinetic reaction mechanism for oxidation of four small alkyl esters in laminar premixed flames

A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate, and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low-pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions for each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules.     

A facile sonochemical route for the synthesis of MoS2/Pd composites for highly efficient oxygen reduction reaction

For the alkaline fuel cell cathode reaction, it is very essential to develop novel catalysts with superior catalytic properties. Here, we report the synthesis of highly active and stable MoS₂/Pd composites for the oxygen reduction reaction (ORR), via a simple, eco-friendly sonochemical method. The bulk MoS₂ was first transformed into single and few layers MoS₂ nanosheets through ultrasonic exfoliation. Then the exfoliated MoS₂ nanosheets served as supporting materials for the nucleation and further in-situ growth of Pd nanoparticles to form MoS₂/Pd composites via ultrasonic irradiation. Cyclic voltammetry and rotating disk voltammetry measurements demonstrate that as-prepared MoS₂/Pd composites which provides a direct four-electron pathway for the ORR, have better electrocatalytic activity, long-term operation stability than commercial Pt/C catalyst. We expect that the present work would provide a promising strategy for the development of efficient oxygen reduction electrocatalyst. In addition, this study can also be extended to the preparation of other hybrid with desirable morphologies and functions.     

方块电阻法原位表征Cu薄膜氧化反应动力学规律

提出并建立了一种基于方块电阻测量的原位表征Cu薄膜氧化反应动力学规律的方法.利用Cu薄膜方块电阻随氧化时间的变化情况，得到氧化产物厚度与氧化时间的关系，反应动力学表征结果符合抛物线规律.还利用不同的氧化反应温度条件和对应的抛物线常数之间的关系得到体系的扩散激活能.结果表明，提出的表征方法适用于Cu薄膜氧化反应体系.     

The study of optimal oxidation time and different temperatures for high quality VO2 thin film based on the sputtering oxidation coupling method

The high quality Vanadium dioxide (VO₂) thin films have been fabricated successfully on sapphire by a simple novel sputtering oxidation coupling (SOC) method. All VO₂ thin film samples exhibit a good metal-insulator transition (MIT) at about 340 K. The optimal oxidation time at different temperatures has been experimentally investigated. We report on the relationship between optimal oxidation time and different temperatures of metal vanadium thin film samples of 101 nm thickness by oxidation in air. It is found that the optimal oxidation time ln(t) as a function of temperature 1/T shows a significant linear relationship among 703 K-783 K, in good agreement with the Wagner's high-temperature oxidation model.     

水辅助下的OH自由基与CH3OOH气相反应机理的理论研究

利用量子化学计算方法对单个水分子不存在与存在的情况下OH自由基与CH3OOH的气相氢抽取反应进行了理论研究。在BHandHLYP/6-311++G(2df,2pd)理论水平下优化了所有驻点的几何构型,在此基础上利用CCSD(T)/cc-pVTZ方法对所有驻点的单点能重新进行了计算。计算结果表明,OH自由基与CH3OOH反应的主要通道是OH自由基抽取CH3OOH中的-OH基团上的H原子。在单个水分子存在的情况下,反应的主要通道没有改变,但是水化过渡态的能量显著地降低,显然单个水分子对OH+CH3OOH反应具有催化效应。     

The influence of polytetrafluorethylene reduction on the capacity loss of the carbon anode for lithium ion batteries

To date, the lithium ion battery has become the focus of secondary battery studies. A considerable capacity loss during the first lithiation of its carbon electrode is a severe drawback of this kind of battery. It has been suggested frequently that the capacity loss was caused by the decomposition of the electrolyte on the surface of the carbon electrode. However, the contribution of binder reduction to this capacity loss has never been considered until now. This paper deals with the binder polytetrafluorethylene (PTFE) reduction and finds that it plays an important part in the capacity loss. It is found that (1) the capacity loss increased with increasing PTFE binder content, (2) the X-ray diffraction peaks corresponding to the PTFE, binder became weaker, while more of the lithium was consumed by the carbon electrode, and disappeared when the consumed amount of lithium exceeded the theoretical value of 1070 mAh per gram of PTFE and (3) the height of the high voltage plateau of the electrochemical titration curves was just a function of storage time, and the length of the plateau was a function of the PTFE content.     

改进的二维分形模型在海面电磁散射中的应用

提出了一种改进的二维分形海面模型，其表面谱函数在空间波数小于基波波数及大于基波波数时分别满足正幂率关系和负幂率关系.通过比较可以发现在不同风速时，改进模型的空间自相关函数及表面轮廓谱和有关文献结果有较好的吻合.在满足Kirchhoff近似条件下推导了改进分形模型的散射系数及散射强度系数的计算公式并进行了数值计算，比较了改进模型和经典模型的后向散射强度系数角分布并详细讨论了它们随入射频率、海上风速和风向的变化. 关键词： 改进分形模型 粗糙海面 电磁散射 Kirchhoff近似     

超声断层扫描数据压缩的时间窗构造及数据提取方法

介绍了一种针对三维超声断层扫描系统的数据压缩方法,该方法通过检测最早的目标反射重构目标表面位置;依据表面位置,计算目标回波信号的起止时间;以此为依据构造时间窗,标明成像算法所需数据在采样序列中存在的时间范围;最终提取有用数据,完成数据压缩。临床数据被用于算法的效果评价。结果表明,该方法可达到平均2.27的压缩率和0.21的压缩率标准差,以及2.25的数据传输加速比。较传统数据压缩方法,该方法只利用回波时域信息,可作为预压缩方法和传统方法结合使用以获得更高的压缩率。     

A physical model for dimensional reduction and its effects on the observable parameters of the universe

We construct a physical model to study the effects of dimensional reduction that might have taken place during the inflationary phase of the universe. The model we propose is a (1 + D)-dimensional (D > 3), nonsingular, spatially homogeneous and isotropic Friedmann model. We consider dimensional reduction to take place in a stepwise manner and interpret each step as a phase transition. Independent of the details of the process of dimensional reduction, we impose suitable boundary conditions across the transitions and trace the effects of dimensional reduction to the currently observable parameters of the universe. In order to exhibit the cosmological features of the proposed model, we construct a (1 + 4)-dimensional toy model for both closed and open cases of Friedmann geometries. It is shown that in these models the universe makes transition into the lower dimension when the critical length parameter l _4,3, which signals dimensional reduction, reaches the Planck length in D = 3. The numerical models we present in this paper have the capability of making definite predictions about the cosmological parameters of the universe such as the Hubble parameter, age and density.     

Diagnosis of deactivation sources for vanadium catalysts used in SO2 oxidation reaction and optimization of vanadium extraction from deactivated catalysts

Physico-chemical analysis (X-ray, FTIR) and/or methanol oxidation reaction test were performed on fresh and deactivated vanadium catalysts used in H₂SO₄ manufacturing. It allowed the diagnosis of catalyst deactivation sources, as well as the processes of regenerating and recycling the worn out catalyst in converter. One of these processes is hydrometallurgical method. It consists in treating the deactivated catalyst with alkaline or acidic reagents and forming vanadate solution. A simple and non-costly operation of chemical attack permits the extraction of vanadium from silica in deactivated catalyst. The extracted vanadium can be used for the confection of regenerated catalysts or metallic tools. After optimization, this method can be used for industrial application.     

电子碰撞原子(e,2e)反应的复极化势

研究包括连续通道等非处理通道的复极化势对(e,2e)碰撞过程三重微分截面的影响,即将耦合通道光学势方法得到的复极化势附加到畸变波玻恩近似方法的畸变势中,在靶态的HF近似下,计算了Ar原子和Ne原子在非共面对称几何条件下(e,2e)反应的三重微分截面.对于较高的入射能量,在实验的误差范围内,计算结果与电子动量谱的实验数据符合较好,复极化势的影响很小;对于较低的入射能量,复极化势的作用明显增大. 关键词： 复极化势 (e;2e)反应 三重微分截面 电子动量谱     

The prediction of the vibration reduction index Kij for brick and concrete rigid junctions

The vibration reduction index, K_ij, is related to the transmission of the vibrational power over a junction between structural elements. Two empirical models are proposed to evaluate K_ij, on the basis of statistical evaluations of numerous in-field tests carried out on rigid junctions between floors made by concrete beams and ribbed slab with brick blocks and brickwork walls, a type of junction that is frequently encountered in Southern European and Mediterranean buildings. These models can be applied in order to calculate the sound insulation properties, such as the normalized impact sound pressure level, , and the apparent sound reduction index, R′, of walls and floors in buildings.The first model allows the single number value of the vibration sound reduction index of a junction to be calculated, on the basis of the real properties of the materials that constitute the junction. A new quantity, the “essential” mass per unit area, was introduced to implement the model.The second model provides an estimation of the K_ij as a function of frequency, subdivided between BB-junction, as ribbed slab with brick blocks floor-brick wall, and CB-junction, i.e. concrete beam-brick wall.     

Near-infrared spectroscopy as a rapid tool for water content analysis in the partial oxidation of ethanol

Abstract

The oxidation of ethanol to acetaldehyde was previously investigated in a continuous flow bench scale reactor using a zirconium-oxide-supported vanadium catalyst. Products were analyzed by near-infrared spectroscopy, a fast and accurate tool for the determination of water, ethanol, and acetaldehyde content. Water content was calibrated by Karl Fischer titration while gas chromatography was used to calibrate ethanol and acetaldehyde contents. Near-infrared spectroscopy is a fast, cost-effective method for the determination of water, ethanol, and acetaldehyde products from partial ethanol oxidation.     

The molecular basis for the behaviour of niobia species in oxidation reaction probed by theoretical calculations and experimental techniques

This paper describes the preparation and use of a new class of materials based on synthetic niobia as catalysts in the oxidation of organic compounds in aqueous medium. The chemical reactions were carried out in the presence of hydrogen peroxide (H₂O₂). The material was characterized with X-ray diffraction, XPS and H₂-TPR (temperature-programmed reduction) measurements. The organic molecule methylene-blue was used in the decomposition study as a probe contaminant. The analysis using the ESI-MS technique showed complete oxidation observed through different intermediates. This suggests the use of niobia species as an efficient Fenton-like catalyst in degradation reactions. Theoretical quantum DFT calculations were carried out in order to understand the degradation mechanism.     

湍流激励下柔性层贴敷加筋板自噪声的特征机理

为了研究湍流激励下柔性层贴敷加筋板自噪声的特征机理,基于湍流边界层壁面脉动压力功率谱模型、周期加筋板弯曲运动方程和固体波动方程以及力平衡与位移连续边界条件,建立了湍流边界层壁面脉动压力激励下柔性层贴敷单向周期加筋板的振动及内噪声物理模型。研究发现:橡胶外贴时对湍流激励下壳板的减振降噪主要依靠橡胶的厚度模态振动。无筋时,橡胶层外贴板较无橡胶贴敷板,主要降低湍流脉动压力的水动力学成分所致结构自噪声,距壳板0.05m时,声压降幅小于3 dB,橡胶外贴加筋板相对于加筋板,对湍流激励结构自噪声的降低基本涵盖整个波数域,距壳板0.7 m处,声压降幅仍然在20 dB左右。肋骨横截面高度或宽度每增大1倍,壳板肋骨处加速度自功率谱级降低3 dB,非肋骨处加速度及板内侧声压自功率谱则基本不变,肋骨间距改变对壳板加速度响应及板内侧声压自功率谱级皆无显著影响。     

Theory of chemical bonds in metalloenzymes XXII: a concerted bond-switching mechanism for the oxygen–oxygen bond formation coupled with one electron transfer for water oxidation in the oxygen-evolving complex of photosystem II

ABSTRACT

QM(UB3LYP)/MM(AMBER) calculations were performed for the locations of the transition structure (TS) of the oxygen–oxygen (O–O) bond formation in the S₄ state of the oxygen-evolving complex (OEC) of photosystem II (PSII). The natural orbital (NO) analysis of the broken-symmetry (BS) solutions was also performed to elucidate the nature of the chemical bonds at TS on the basis of several chemical indices defined by the occupation numbers of NO. The computational results revealed a concerted bond switching (CBS) mechanism for the oxygen–oxygen bond formation coupled with the one-electron transfer (OET) for water oxidation in OEC of PSII. The orbital interaction between the σ-HOMO of the Mn(IV)₄–O₍₅₎ bond and the π*-LUMO of the Mn(V)₁=O₍₆₎ bond plays an important role for the concerted O–O bond formation for water oxidation in the CaMn₄O₆ cluster of OEC of PSII. One electron transfer (OET) from the π-HOMO of the Mn(V)₁=O₍₆₎ bond to the σ*-LUMO of the Mn(IV)₄–O₍₅₎ bond occurs for the formation of electron transfer diradical, where the generated anion radical [Mn(IV)₄–O₍₅₎]^-? part is relaxed to the ?Mn(III)₄?…?O₍₅₎^- structure and the cation radical [O₍₆₎=Mn(V)₁]⁺ ? part is relaxed to the ⁺O₍₆₎–Mn(IV)₁? structure because of the charge-spin separation for the electron-and hole-doped Mn–oxo bonds. Therefore, the local spins are responsible for the one-electron reductions of Mn(IV)₄->Mn(III)₄ and Mn(V)₁->Mn(IV)₁. On the other hand, the O₍₅₎^- and O₍₆₎⁺ sites generated undergo the O–O bond formation in the CaMn₄O₆ cluster. The Ca(II) ion in the cubane- skeleton of the CaMn₄O₆ cluster assists the above orbital interactions by the lowering of the orbital energy levels of π*-LUMO of Mn(V)₁=O₍₆₎ and σ*-LUMO of Mn(IV)₄–O₍₅₎, indicating an important role of its Lewis acidity. Present CBS mechanism for the O–O bond formation coupled with one electron reductions of the high-valent Mn ions is different from the conventional radical coupling (RC) and acid-base (AB) mechanisms for water oxidation in artificial and native photosynthesis systems. The proton-coupled electron transfer (PC-OET) mechanism for the O–O bond formation is also touched in relation to the CBS-OET mechanism.     

A method for determining the sound reduction index of precast panels based on point mobility measurements

Precast panels are widely used for the construction of large industrial buildings, trade centres and apartment houses. These buildings have to comply with prescribed noise and thermal requirements, so the possibility to accurately estimate the sound reduction index of such panels is of vital importance. The sound reduction index can be determined through measurements carried out in a laboratory or on an already mounted real-scale panel, but both solutions present problems. For example, precast structures consisting of two concrete panels coupled via an interlayer can be very bulky and heavy, and measurements in standard sound transmission laboratories may be impossible to carry out. In some countries, predictions based on theoretical models are accepted in lieu of measurements. Following this approach, the application of simple models, not accounting for the influence of coincidence and of losses, is not sufficient to make acceptable predictions. In this paper, an alternative method to estimate the sound reduction index of precast panels is proposed. Different panels have been considered in the study, each of which has been modelled by a mathematical representation found in the literature. It will be shown that all of these models can be synthesised by a common mathematical formulation, allowing the sound reduction index to be determined from point mobility measurements. The effectiveness of the new method has been investigated by comparing predicted and measured results, obtained in a sound transmission laboratory satisfying existing ISO standards.     

Ultrasonic-assisted reduction for facile synthesis of ultrafine supported Pd nanocatalysts by hydroxyl groups on the surfaces of layered double hydroxides and their catalytic properties

Layered double hydroxide (LDH)-supported Pd nanocatalysts (Pd/LDH-OH) were prepared by ultrasonic-assisted reduction at 30 °C using an ultrasonic bath at a frequency of 25 kHz and an input power of 400 W for 30 min without the addition of any stabilizing reagent or chemical reductant, using LDH with a layered structure and interparticle mesoporosity as the reductant and carrier. This kind of pore structure allows ultrasound waves to spread inside the pore and make ultrasound directly act on the surface hydroxyl groups of LDH, producing highly reductive free radicals (H). The reductive free radicals rapidly reduced Pd²⁺ to Pd⁰, forming ultrafine Pd nanoparticles (PdNPs) with a particle size distribution of 1.85 nm–3.45 nm and an average particle size of 2.52 nm. The surface hydroxyl groups were converted to exposed oxygen groups after dissociation of hydrogen radicals, which is beneficial for anchoring and dispersing the resultant PdNPs. The resultant PdNPs were uniformly dispersed on the surface of the LDH carrier. The yield of the Suzuki coupling reaction between 4-bromotoluene and phenylboronic acid catalyzed by Pd/LDH-OH at 60 °C was 95.49% for 5 min and the TOF was 190.98 min⁻¹. After repeated for 5 times, the yield was maintained at 84.59%. The prepared Pd/LDH-OH nanocatalyst and the catalytic system are useful for Suzuki-Miyaura coupling reactions of N- and S-heterocyclic substrates. This provides an efficient and green approach for the preparation of supported nanopalladium catalysts.