氢气对薄反应区湍流火焰详细火焰结构影响研究

氢是一种非常有前景的清洁可再生能源载体.掺氢燃料预混稀燃是当前开发清洁高效的低排放燃气轮机最重要的能源转化方式之一。本文基于预混CH₄/H₂/air本生灯火焰,对氢气掺混影响下的湍流火焰详细火焰结构进行了测量和表征。实验采用CH₂O和OH基平面激光诱导荧光(PLIF,Planar Laser Induced Fluorescence)同步测量技术,获得了火焰预热区、反应区以及已燃区的详细火焰结构信息。本文对反应区和预热区火焰厚度进行了提取和统计。研究表明,氢气对火焰反应区、预热区均有明显作用。结果表明,掺氢小幅度增厚反应区厚度,但能够比较明显地降低预热区厚度。     

Quantitative Measurements of Individual Polycyclic Aromatic Hydrocarbons in a Mixture by Coherent Anti-Stokes Raman Spectrometry

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) was used to obtain Raman spectra of selected polycyclic aromatic hydrocarbons (PAHs) composed of between three and seven fused rings when the compounds were pumped in the resonance and pre-resonance regions, a simple mixture of three PAHs could be optically separated through the wavelength selectivity of the resonant enhancement process. The spectrum from a component in the mixture and the spectrum of each pure component showed no significant differences when pumped at the same wavelength. Finally, lineshape analysis performed on the CARS spectra facilitated comparisons between classes of compounds and for quantitative purposes.     

氧化石墨烯/中空纤维-固相微萃取分析环境水中非甾体抗炎药的残留

建立了氧化石墨烯(GO)与中空纤维(HF)相结合的固相微萃取(GO-HF-SPME)方法并与高效液相色谱(HPLC)联合用于分析环境水中两种非甾体抗炎药(尼美舒利、塞来昔布)的残留。通过红外光谱(FT-IR)、扫描电镜(SME)对GO进行表征。优化并考察了GO的质量、HF的长度、pH、萃取时间、搅拌速度以及解吸附条件对GO-HF-SPME萃取效率的影响。在最佳萃取条件下,尼美舒利和塞来昔布的富集倍数分别为240倍和44倍,且质量浓度在10~500 ng/mL范围内呈良好的线性关系,检出限分别为0.5 ng/mL和2.5 ng/mL,加标回收率介于87.0%~93.5%之间。方法已用于分析环境水中尼美舒利和塞来昔布的残留。     

Octanuclear Ni4Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2Ln2 Cubes: Syntheses,Structures, and Magnetic Properties

A family of 3d–4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL^?) and in situ generated ancillary bridge driven self‐assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol‐based ditopic ligand anion of 2‐[{(2‐hydroxypropyl)imino}methyl]‐6‐methoxyphenol (H₂L) in MeCN‐MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni‐4f coordination aggregates from two Ni₂Ln₂ cubanes. Single‐crystal X‐ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni₂Ln₂O₄] heterometallic cubanes [Ni₂Ln₂(HL)₂(μ₃‐OH)₂(OH)(OAc)₄]⁺ (Ln=Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ) and Yb ( 5 )). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)₂ bridges. Variable temperature magnetic study reveals weak coupling between the Ni²⁺ and Ln³⁺ ions. For the Tb ( 2 ) and Dy ( 3 ) analogs, the compounds are SMMs without an applied dc field, whereas the Gd ( 1 ) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln³⁺ ions is central to display the SMM behavior within this structurally intriguing family of compounds.     

Organic UV filters in marine environments: An update of analytical methodologies,occurrence and distribution

Ultraviolet filters (UV Filters) are compounds that are widely employed in personal care products such as sunscreens to protect the skin from sun damage, but they are also added to other products, such as food packaging, plastics, paints, textiles, detergents, etc. The continuous use of these products causes the release of a substantial amount of these products into the marine environment through direct input or wastewater discharge, and thus they are becoming an important class of contaminants of emerging concern. A correlation between their occurrence and different negative effects on marine biota has been reported.Taking into account all the possible impacts on the environment, knowledge of their presence and distribution in the different compartments of the ecosystems, ranging from waters and sediments to aquatic organisms, which potentially suffer from bioaccumulation and biomagnification processes, is essential. High concentrations of ultraviolet filters have been found in samples collected from across the entire planet, even in polar regions, revealing their global distribution.Therefore, interest in the sensitive determination of ultraviolet filters in several marine matrices has increased. In this article, an overall review of the more recently reported analytical chemistry methods for identifying and quantifying these compounds in marine environmental samples is presented. We compare and discuss the potential advantages and disadvantages of every step involved in the analytical procedure, including the pre-treatment, treatment and extraction processes that are required to avoid matrix effects. Moreover, we describe the worldwide occurrence and distribution of those most important UV filters.     

Effects of curing agents and modified graphene oxide on the properties of XNBR composites

This paper investigates the effects of crosslinking methods on the incorporation of graphene oxide (GO) in carboxylated nitrile butadiene rubber (XNBR) in the process of producing nanocomposites for chemical-resistant protective clothing and gloves. The novel aspect of the study is a comprehensive approach involving both unmodified GO as well as GO that was carboxylated to increase its affinity to XNBR and to facilitate its application. The nanostructure of XNBR composites was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FTIR) was used to elucidate the chemical structure of the composites. Thermal stability studies were performed using differential scanning calorimetry (DSC). The barrier properties of the composites were determined based on swelling, crosslinking density, and permeation by mineral oils. The mechanical tests included resistance to puncture and abrasion, stress at strain, and tensile strength. Contact angle was measured to determine the degree of hydrophobicity of the obtained composites.AFM and SEM images revealed the effects of different curing agents (sulfur, magnesium oxide, or a hybrid system) as well as GO type on the surface morphology of XNBR composites. The type of curing agent was found to affect the kind of crosslinks formed and their spatial network structure, as confirmed by FTIR. The DSC curves showed that the crosslinking methods of XNBR did not affect glass transition temperature, but led to large changes observed in the temperature range of 130–220 °C.The type of crosslinking method affected the degree of swelling. It was found that the incorporation of carbon nanofillers led to an improvement in the abrasion and puncture resistance as well as tensile strength of XNBR composites. The water contact angle of the composites indicated hydrophobicity. The properties of XNBR composites containing GO revealed their substantial application potential in protective clothing.     

Solvent-Free Knoevenagel Condensation over Cobalt Hydroxyapatite

The Knoevenagel condensation between various aldehydes (benzaldehyde, 1-naphthaldehyde, p-bromobenzaldehyde and p-methoxybenzaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent free condition in the presence of cobalt hydroxyapatite (CoHAp), as a catalyst. Good to excellent yields (35–96%) were obtained. The catalyst is found to be superior over fluorapatite and several other heterogeneous catalysts. The catalyst can be recycled at least 3 times.     

Environmental‐Confinement‐Induced Stability Enhancement of Chiral Molecules

We computationally study the transition process of a chiral difluorobenzo[c]phenanthrene (DFBcPh) molecule within non‐polar fullerene C₂₆₀ to explore the confinement effect. We find blue‐shifts in the infrared and Raman spectra of the molecule inside the fullerene relative to those of isolated systems. Six types of spectrum features of the molecule appear in the 0–60 cm^?1 band. Interestingly, the energy barrier of the chiral transformation of the molecule is elevated by 15.88 kcal mol^?1 upon the confinement by the fullerene, indicating improvement in the stability of the enantiomers. The protection by C₂₆₀ lowers the highest occupied molecular orbital energy level and lifts the lowest unoccupied molecular orbital energy level of the chiral molecule such that the chiral molecule is further chemically stabilized. We concluded that the confinement environment has an impact at the nanoscale on the enantiomer transformation process of the chiral molecule.     

Heterogeneous credit portfolios and the dynamics of the aggregate losses

We study the impact of contagion in a network of firms facing credit risk. We describe an intensity based model where the homogeneity assumption is broken by introducing a random environment that makes it possible to take into account the idiosyncratic characteristics of the firms. We shall see that our model goes behind the identification of groups of firms that can be considered basically exchangeable. Despite this heterogeneity assumption our model has the advantage of being totally tractable. The aim is to quantify the losses that a bank may suffer in a large credit portfolio. Relying on a large deviation principle on the trajectory space of the process, we state a suitable law of large numbers and a central limit theorem useful for studying large portfolio losses. Simulation results are provided as well as applications to portfolio loss distribution analysis.     

Automated Mössbauer spectroscopy in the field and monitoring of fougerite

A special experimental setup for in-field applications was developed at Mainz. It incorporates hardware for automated positioning of the Mössbauer sensor head, a Plexiglas tube, and a modified version of the space proven Miniaturized Mössbauer Spectrometer MIMOS II (Klingelhöfer et al., Science, 306:1740–1745, 2004; Klingelhöfer et al., J. Geophys. Res., 108(E12):8067, 2003; Klingelhöfer et al., Hyperfine Interact. 144/145:371–379, 2002; Génin et al., Solid State Sci., 7:545–572, 2005). MIMOS operates in backscattering geometry, thus no sample preparation is required. Also dedicated software for running measurement sequences (e.g., different depth positions at different times etc.) was developed. The setup can work autonomously up to several weeks in the field. Preliminary results confirm that fougerite mineral found in hydromorphic soils is Fe^II–III hydroxycarbonate green rust.