Polarized Raman spectra,thermodynamic functions and bidders to internal rotation of 2,3-dimethoxy toluene

Polarized Raman spectra of 2,3-dimethoxy toluene have been recorded in the region 50–4000 cm⁻¹ and IR spectra in the region 200–4000 cm⁻¹. All the 63 (40a′ + 23a″) normal modes of vibration have been assigned assuming a C_s point group. Consistent assignments for the internal modes of vibration of methyl (CH₃) and methoxy (OCH₃) groups have been proposed. In addition thermodynamic functions have been computed over the temperature range 100–1500 K on a MIGHTY II computer and barriers to internal rotations for the three methyl (CH₃) tops and the two methoxy (OCH₃) tops about their respective axes have been determined, using the assigned torsional frequencies and assumed structural parameter for the 2,3-dimethoxy toluene. The barrier heights have been found to be greater than 2.5 kcal mol⁻¹ for all five tops.     

Electronic cooling in superconducting tunnel junctions

The cooling power provided by the current through a superconductor/insulator/superconductor tunnel junction is studied theoretically. The influence of non-equilibrium distributions of the quasi-particles on the heat flow is analysed within a simple relaxation model. A superconducting gap enhancement can be explained within the equilibrium as well as the non-equilibrium model.     

Poly(amide-imide)/TiO2 nano-composite gas separation membranes: Fabrication and characterization

Nano-composite membranes based on a fluorinated poly(amide-imide) and TiO₂ were fabricated by a sol-gel method. Permeability data for gases such as O₂, N₂, CO₂, H₂ and CH₄ were collected as a function of pressure and temperature. With the exception of CO₂ and H₂, all other gases exhibited higher activation energies for the nano-composite membrane when compared with the pure poly(amide-mide), consistent with the picture of a more rigid or denser structure as suggested by the physical characterization data. The decrease in the activation energy for permeation in the case of CO₂ and H₂ has been attributed to specific interactions of these gases with the TiO₂ domains. Significant improvements in permselectivies of the poly(amide-imide) membrane have been observed in view of the volume percentage of the TiO₂ incorporated into the polymer matrix.     

基于目标与环境FD模型的多特征检测算法适应性评估

智能变形、变色、变温、变谱技术发展趋势下,低特征目标加速实现与自然地物背景的特征融合,导致复杂自然背景环境下低散射、微反射、弱辐射目标的检测与评估愈发困难,特定场景下潜在威胁目标的检测方法快速决策与准确评估成为了难题.为了提升离散目标、伪装目标、弱小目标、异常目标等低特征目标与复杂自然背景环境融合场景下的多特征检测算法...     

Oxidation chemistry and biochemistry of some biologically important purines and indoleamines

The electrochemical oxidation of 7-methyluric acid and 5,6-dihydroxytryptamine (5,6-DHT) in aqueous solutions has been studied. The oxidation products have been separated and characterized using melting point, mass, ¹H nuclear magnetic resonance and spectral studies, and tentative mechanisms for the oxidation have been suggested. One of the oxidation products of 5,6-DHT, i.e. 2,7′-bi(5,6-DHT), has been found to produce a substantial neurotoxic effect in mice brain.     

A contribution to the study of matrix effects in the analysis of solid samples by D. C. glow discharge mass spectrometry

Relative Sensitivity Factors (RSF) for the analysis of 22 elements by glow discharge mass spectrometry have been determined from the multiple determination of 19 reference materials representing steels, Ni-based heat resisting alloys, copper, aluminium, molybdenum and indium by using an Ar/0.2 vol. % H₂ mixture as a filler gas. The measurements were made by using the VG 9000 glow discharge mass spectrometer. For all the materials analyzed, the relative variations of these factors were reduced by more than a factor of 2 when the Ar/H₂ mixture was substituted to the pure argon. In addition, the proposed technique greatly decreases the matrix effects, thus allowing the determination of the elemental composition of metallic samples without needing to use standard reference materials.     

Topology Controlled All-(Meth)acrylic Thermoplastic Elastomers by Multi-Functional Lewis Pairs-Mediated Polymerization

It remains challenging to synthesize all-(meth)acrylic triblock thermoplastic elastomers (TPEs), due to the drastically different reactivities between the acrylates and methacrylates and inevitable occurrence of side reactions during polymerization of acrylates. By taking advantage of the easy structural modulation features of N-heterocyclic olefins (NHOs), we design and synthesize strong nucleophilic tetraphenylethylene-based NHOs varying in the number (i.e. mono-, dual- and tetra−) of initiating functional groups. Its combination with bulky organoaluminum [ⁱBuAl(BHT)₂] (BHT=bis(2,6-di-^tBu-4-methylphenoxy)) constructs Lewis pair (LP) to realize the living polymerization of both acrylates and methacrylates, furnishing polyacrylates with ultrahigh molecular weight (M_n up to 2174 kg ⋅ mol⁻¹) within 4 min. Moreover, these NHO-based LPs enable us to not only realize the control over the polymers’ topology (i.e. linear and star), but also achieve triblock star copolymers in one-step manner. Mechanical studies reveal that the star triblock TPEs exhibit better mechanical properties (elongation at break up to 1863 % and tensile strength up to 19.1 MPa) in comparison with the linear analogs. Moreover, the presence of tetraphenylethylene group in the NHOs entitled the triblock TPEs with excellent AIE properties in both solution and solid state.     

木蜡油涂饰对檀香紫檀易混树种的红外光谱影响分析

卢氏黑黄檀和染料紫檀木材特征与檀香紫檀相似,特别是两者经过加色精的木蜡油涂饰后,用肉眼很难与珍贵的檀香紫檀分辨。市场上销售的很多红木家具为了达到防腐、防尘、防开裂的性能以及提高红木表面光泽度和显现珍贵木材的纹理,大都进行了木蜡油表面涂饰加工,因而只研究木材本身的鉴别不能满足市场需求。借助红外光谱（FTIR）结合二阶导数红外光谱（SDIR）和二维相关红外光谱（2D-IR）技术,对经过木蜡油涂饰的檀香紫檀（Pterocarpus santalinus）、染料紫檀（P.tinctoricus Welw）和卢氏黑黄檀（Dalbergia louuelii）进行了红外光谱分析。通过打磨-涂底油-打磨-涂面油-干燥的涂饰工艺对3个树种进行表面涂饰。分别取3个树种素材的木粉和经过表面涂饰的木材表面的木粉进行FTIR,SDIR和2D-IR三级鉴别分析,同时测定了木蜡油的FTIR谱图。结果表明：(1）木蜡油FTIR谱图在2 925,1 733,1 465和1 378 cm-1较强的特征峰出峰位置与3个树种木材本身的出峰位置基本重合,且在2 854 cm-1处归属于亚甲基C-H对称伸缩振动,1 233 cm-1处归属于羧基C-O伸缩振动,729 cm-1处归属于长链的亚甲基C-H弯曲振动的特征峰在涂饰后三种样品的FTIR谱图中有相同的体现,说明木蜡油涂饰未对3个树种红外谱图的特征峰产生影响;3个树种表面涂饰前后FTIR谱图的相关系数同时可以对木蜡油涂饰未对3个树种的特征峰产生影响进行佐证;(2）FTIR谱图在1 595,1 060和836 cm-1处可以将染料紫檀与檀香紫檀和卢氏黑黄檀两个树种区分开;SDIR谱图可以在1 551 cm-1将卢氏黑黄檀区分开,并能进一步对染料紫檀的特征峰进行验证;在2D-IR光谱中,在1 425~1 800和850~1 300 cm-1两个波段范围,檀香紫檀的自动锋明显区别于其他两个树种,在1 250 cm-1处归属于醚类化合物的吸收峰可以将檀香紫檀区分开。目前红木识别主要利用木材解剖方法,表面涂饰大多集中在木材材色变化研究。借助红外光谱技术,最终利用各个树种和木蜡油在红外光谱谱图中不同的特征峰体现的官能团差异直接推测特征成分的含量差异,无须测定其特征成分的具体物质,进而实现准确、快速地把经木蜡油表面涂饰的檀香紫檀及与其易混淆的染料紫檀和卢氏黑黄檀区分鉴别。     

Oscillatory cool flame combustion behavior of submillimeter sized n-alkane droplet under near limit conditions

This paper reports simulation results of oscillatory cool flame burning of an isolated, submillimeter sized n-heptane (n-C₇H₁₆) droplet in a selectively ozone (O₃) seeded nitrogen-oxygen (N₂-O₂) environments at atmospheric pressure. An evolutionary one-dimensional droplet combustion code encompassing relevant physics and detailed chemistry was employed to explore the roles of low-temperature chemistry, O₃ seeding, and dynamic flame structure on burning behaviors. For X_O2= 21% and a range of selective ozone seeding, near-quasi-steady cool flame burning is achieved directly (without requiring hot flame initiation and radiative extinction). Under low oxygen index conditions, but with significant O₃ seeding (X_O3 = 5%), a nearly quasi-steady cool flame is initially established that then transitions to a dynamically oscillating cool flame burning mode which continues until the droplet is completely consumed. It is found that the oscillation occurs as result of a initial depletion of fuel vapor-oxidizer layer evolving near the droplet surface and its dynamic re-establishment through liquid vaporization and vapor/oxidizer transport. A kinetic analysis indicates that the dynamic competition between the reaction classes- (a) degenerate chain branching and (b) chain termination/propagation - along with continuous fuel and oxygen leakage through the flame location contributes to an oscillatory burning phenomena of ever-increasing amplitude. Analysis based on single full-cycle of oscillatory burning shows that the reaction progression matrices (evolution of heat and species) for QOOH➔chain propagation/termination reactions (here, Q = C₇H₁₄-) directly scales with the gas phase temperature field. On the contrary, the QOOH➔degenerate branching reactions undergoes three distinct stages within the same oscillatory cycle. The coupled flame dynamics and kinetics suggest that in the oscillatory burning mode, kinetic processes dynamically cross through conditions characterizing the negative temperature coefficient (NTC) turnover temperature, separating low temperature and NTC kinetic regimes. In addition, a parametric study is conducted to determine the role of O₃ seeding level on the observed oscillation phenomena.