UV spectral characterization of a smectic-C liquid crystal: Theoretical support to the experiment

In the present article, UV spectral characterization of a smectic-C liquid crystal 4,4′-bis(n-alkoxy)azoxybenzene (n = 14) (C₄₀H₆₆N₂O₃) has been carried out. Structure of the molecule has been optimized using the Density functional B3LYP with 6-31+G (d) basis set using crystallographic geometry as input. The absorption spectra have been estimated in the UV region by employing the DFT method, semiempirical CNDO/S and INDO/S parameterizations. The oscillator strength (f) and vertical transition energy (E_V) have been reported corresponding to absorption wavelength (λ_max). These values have been compared with the experimental value reported in the literature to offer theoretical support to the experimental value. Further, some electrochemical properties have been reported for the molecule.     

Rate and Product Studies in the Solvolyses of Two Cyclic Phosphorochloridate Esters

Kinetic and product studies of the solvolyses of acyclic phosphorochloridates are extended to two cyclic diesters, 2-chloro-1,3,2-dioxaphospholane-2-oxide (1) and 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane-2-oxide (2). Slightly faster solvolyses are observed for 1 than for the acyclic dimethyl phosphorochloridate (3), and 2 solvolyzes somewhat slower than 3. An extended Grunwald–Winstein equation treatment shows similar sensitivities to changes in solvent nucleophilicity and solvent ionizing power for 1, 2, and 3, and a concerted S_N2 attack is proposed in each case. Product studies for the solvolyses of 2 in aqueous alcohols are presented.

     

AB CROSSLINKED POLYURETHANES THROUGH IONIC CROSSLINKING: INFLUENCE OF CROSSLINKING NETWORKS ON PHYSICO CHEMICAL PROPERTIES

Isocyanate-terminated prepolymers were synthesized using poly(tetramethylene oxide)glycol of molecular weight 1000 (PTMG₁₀₀₀) with tolylene-2,4-diisocyanate (TDI). The prepolymers were chain extended with N-methyldiethanolamine (N-MDEA) to form polyurethanes containing tertiary nitrogen. These polyurethanes were crosslinked with bromine terminated polyurethane, poly(urethane-imide), and poly(urethane-siloxane) through the formation of cationomers at tertiary nitrogen sites across the backbone polyurethanes.

The crosslinked cationomeric polyurethanes were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), mechanical analyses, (static and dynamic), and static contact angles measurements. FTIR spectral studies confirms the formation of bromine terminated poly(urethane-imide) and poly(urethane-siloxane), as well as quaternization of the tertiary nitrogen which leads to crosslinking. A comparison of thermal stabilities of crosslinked polymers with respect to the chemical nature of bromine terminated prepolymers (BTP) indicates improved thermal stability for poly(urethane-imide) based ABCP. Stress-strain analysis shows high elongation values for poly(urethane-siloxane) and poly(urethane-imide) based ABCPs. Dynamic mechanical analysis reveals better damping for poly(urethane- siloxane) based AB crosslinked polymers.     

Calorimetric Estimation Employing the Unscented Kalman Filter for a Batch Emulsion Polymerization Reactor

Reaction calorimetry is a very useful tool to monitor exothermic polymerization reactions as it is based on the estimation of the heat generated by the reaction. The objective of this work is to analyze the performance of an unscented Kalman filter (UKF) for online monitoring of batch vinyl acetate emulsion polymerization reactions. Reactions are performed in isoperibolic and isothermal conditions. The UKF is compared to an extended Kalman filter that has a very poor performance. The results show that the UKF is able to provide good estimates for the conversion, for the reactor and jacket temperatures, for the overall heat transfer coefficient between the reaction medium and the jacket, and for the heat loss from the jacket to the surroundings.

     

Absolute configuration assignment made easier by the VCD of coupled oscillating carbonyls: the case of (−)-propanedioic acids, 2-(2,3)-dihydro-3-oxo-1H-isoindol-1-yl)-1,3-dimethyl ester

Depending on their relative orientation, coupled oscillating carbonyl groups provide a VCD spectrum with a characteristic CO bond stretching region showing a strong bisignate VCD feature, which can be readily predicted adopting long available semiempirical methods. The extended coupled oscillator (ECO) formalism has been used to assign the absolute configuration of a recently synthesized chiral 3-substituted isoindolinone. The prediction of (S) configuration for the (−) enantiomer has been confirmed by quantum mechanical calculations.     

Trace gas detection of benzene,toluene, p-, m- and o-xylene with a compact measurement system using cantilever enhanced photoacoustic spectroscopy and optical parametric oscillator

A compact measurement system based on a novel combination of cantilever enhanced photoacoustic spectroscopy (CEPAS) and optical parametric oscillator (OPO) was applied to the gas phase measurement of benzene, toluene, and o-, m- and p-xylene (BTX) traces. The OPO had a band width (FWHM) of 1.3 nm, was tuned from 3237 to 3296 nm in steps of 0.1 nm and so spectra of BTX at different concentrations were recorded. The power emitted by the OPO increased from 88 mW at 3237 nm to 103 mW at 3296 nm. The univariate detection limits (3σ, 0.951 s) for benzene, toluene, p-, m- and o-xylene at 3288 nm were 12.0, 9.8, 13.2, 10.1 and 16.0 ppb, respectively. Multivariate data analysis using science-based calibration was used to resolve the interference of the analytes. The multivariate detection limits (3σ, 3237–3296 nm, 591 spectral points each 0.951 s) for benzene, toluene, p-, m- and o-xylene in the multi-compound sample, where all other analytes and water interfere were 4.3, 7.4, 11.0, 12.5 and 6.2 ppb, respectively. Without interferents, the multivariate detection limits varied between 0.5 and 0.6 ppb. The sum of the cross-selectivities (3237–3296 nm, 591 spectral points, each 0.951 s) per analyte were below 0.05 ppb/ppb, with an average of 0.038 ppb/ppb. The cross-selectivity of water to the analytes was on average 1.22 × 10⁻⁴ ppb/ppb. The OPO is small in size (L × W × H 125 × 70 × 45 mm), commercially available, and easy to operate and integrate to setups. The combination with sensitive CEPAS enables compact measurement systems for industrial as well as environmental trace gas monitoring.     

END样本最近邻密度估计的强相合速度

本文研究了扩展负相依(END)样本最近邻密度估计的强相合性问题.利用END序列的Bernstein型不等式和截尾的方法,获得了END样本最近邻密度估计的强相合速度,推广了NA样本和ND样本最近邻密度估计的相应结果.     

Generalized Fourth-Order Decompositions of Imaginary Time Path Integral: Implications of the Harmonic Oscillator

The imaginary time path integral formalism offers a powerful numerical tool for simulating thermodynamic properties of realistic systems. We show that, when second-order and fourth-order decompositions are employed, they share a remarkable unified analytic form for the partition function of the harmonic oscillator. We are then able to obtain the expression of the thermodynamic property and the leading error terms as well. In order to obtain reasonably optimal values of the free parameters in the generalized symmetric fourth-order decomposition scheme, we eliminate the leading error terms to achieve the accuracy of desired order for the thermodynamic property of the harmonic system. Such a strategy leads to an efficient fourth-order decomposition that produces third-order accurate thermodynamic properties for general systems.     

类Liu系统在水声微弱信号检测中的应用研究

利用三阶混沌系统构造了一种新的微弱信号检测系统——类Liu系统, 对类Liu 系统进行了深度的理论分析. 类Liu系统中, 当输入待测信号幅值大于某临界值时, 系统可达到平衡点S₀, S₀中系统变量x平衡于摄动力信号, 系统变量y, z收敛于零态, 且S₀ 对应的Lyapunov指数小于零. 通过Matlab仿真、Multisim电路仿真以及实际电路证明了类Liu系统的周期态收敛性及广域检测性, 解决了传统Duffing系统进行微弱信号检测时周期态不收敛、只能进行窄域检测等问题, 同时谱级信噪比范围仍可达-46.57 dB. 类Liu系统采用了全新的设计理念, 具有较高的实用价值, 对未来海洋物联网中的水声通信有一定参考价值.