基于神经网络混合整数线性规划的精馏分离序列优化综合

针对精馏分离序列综合问题,运用图论方法研究网状超级结构。结合相对费用函数建立了混合整数线性规划模型。开发了面向大规模精馏分离序列综合问题的自动求解程序,实现了10组分精馏分离序列综合问题的成功解算,探索了神经网络混合整数线性规划的思想框架。     

Linear segmented polyurethanes: I. A kinetics study

This work investigates the two‐step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4‐butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (¹H‐NMR), and size exclusion chromatography. ¹H‐NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following “effective” rate constants: k₁ = 1.07 × 10^?3 L mol^?1 s^?1 for the prepolymerization; and k₂ = 1.94 × 10^?4 L mol^?1 s^?1 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The ¹H‐NMR measurements also enabled to estimate the evolution (with extent of reaction) of the number‐average number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45747.     

Polyfurans: A Computational Study

Polyfurans and furan-based polymers have recently emerged as a new class of conjugated materials. We undertook the first comprehensive computational study of polyfurans, especially doped polyfurans, and systematically compared their properties with those of the corresponding polythiophenes. Parent polyfuran has higher highest occupied crystal orbit and lowest unoccupied crystal orbit energies (by 0.25 and 0.61 eV, respectively), as well as a higher band gap (by 0.36 eV) and significantly larger twisting energy than that of polythiophenes. Doping of polyfuran and polythiophene was less exothermic than polyselenophene in all cases. For thermodynamic reasons, polyfurans should be easier to dope lightly than polythiophenes, whereas at heavy doping levels polyfurans and polythiophenes should be doped with similar ease.     

Computational Modeling of Silicon Nanoparticle Synthesis: I. A General Two-Dimensional Model

A two-dimensional model has been developed for silicon nanoparticle synthesis by silane thermal decomposition driven by laser heating in a tubular reactor. This fully coupled model includes fluid dynamics, laser heating, gas phase and surface phase chemical reactions, and aerosol dynamics which includes particle transport and evolution by convection, diffusion, thermophoresis, nucleation, surface growth, and coagulation processes. A moment method, based upon a lognormal particle size distribution, and a sectional method are used to model the aerosol dynamics. The simulation results obtained by the two methods are compared. The sectional method is capable of capturing the bimodal behavior that occurs locally during the process, while the moment method is computationally more efficient. The effect of operating parameters, such as precursor concentration, gas phase composition, inlet gas velocity and laser power input, on the characteristics of the particles produced are investigated. Higher temperature generates more large particles with higher precursor conversion. Shorter residence time, from high inlet velocity, produces more small particles at the cost of lower precursor conversion. Increasing H₂ concentration suppresses particle formation by reducing the rates of gas phase and surface reactions, leading to fewer and smaller particles. In addition, the relative importance of the interconnected mechanisms involved in the particle formation is considered. The results make clear that spatial variations in reaction conditions are the primary source of size polydispersity and generation of non lognormal overall size distributions in a laser-driven process like that considered here.     

A Mixed Coding Scheme of a Particle Swarm Optimization and a Hybrid Genetic Algorithm with Sequential Quadratic Programming for Mixed Integer Nonlinear Programming in Common Chemical Engineering Practice

In this paper, mixed integer nonlinear programming (MINLP) is optimized by PSO_GA–SQP, the mixed coding of a particle swarm optimization (PSO), and a hybrid genetic algorithm and sequential quadratic programming (GA–SQP). The population is separated into two groups: discrete and continuous variables. The discrete variables are optimized by the adapted PSO, while the continuous variables are optimized by the GA–SQP using the discrete variable information from the adapted PSO. Therefore, the population can be set to a smaller size than usual to obtain a global solution. The proposed PSO_GA–SQP algorithm is verified using various MINLP problems including the designing of retrofit heat exchanger networks. The fitness values of the tested problems are able to reach the global optimum.     

A Systematic Computational Study on Flavonoids

17 selected flavones derivatives, flavonoids, were analyzed through a systematic B3LYP/6-311++G** computational study with the aim of understanding the molecular factors that determine their structural and energetic properties in gas phase. Flavonoids were selected in a systematic way to infer the effect of the number and relative positions of hydroxyl groups on molecular properties. Different conformers for each flavonoid were analyzed and the strength and topology of the intramolecular hydrogen bonds studied through the computation of the corresponding torsional profiles. Atoms in a Molecule, and Natural Bond Orbital methodology was applied to the analysis of charge distribution along the studied molecules, and the intramolecular hydrogen bonds. Molecular shapes were studied through full geometry optimization, and the position of the catechol ring analyzed through dihedral scans.     

Degradation on polyacrylamides. Part I. Linear polyacrylamide

The stability of linear polyacrylamides (PAAM) under thermal and irradiation conditions were investigated. The study showed that PAAm is stable under fluorescent lights and does not release any detectable acrylamide (AAM) in hot aqueous solution at 95 °C. Hydrolysis of side-chain amide groups to acid groups was observed during the thermal aqueous degradation. Under UV irradiation, small levels of released AAm were observed; however they are generally below 50 parts per million repeat monomer units in the polymer. A drop in viscosity is also observed. This indicates that the acrylamide released is due to chain scission, not a unzipping of the polymer chain. Methods of purifying a linear PAAM are also discussed.     

多组分混合烷烃分离序列的合成优化研究

多组分精馏序列的研究是降低多塔精馏分离能耗的重要手段.本文采用双塔精馏分离正丁烷、正戊烷和正己烷混合物,对两种分离序列进行比选,两种工艺分别记为工艺a和工艺b,以产品纯度相同与能耗最小化为依据,采用Aspen plus对两种工艺进行模拟优化,得出工艺a的总能耗为1383.53 kW,工艺b的总能耗为1151.94 kW...     

Toughness measurement on ball specimens. Part I: Theoretical analysis

A new toughness test for ball-shaped specimens is presented. In analogy to the “Surface Crack in Flexure”-method the fracture toughness is determined by making a semi-elliptical surface crack with a Knoop indenter into the surface of the specimen. In our case the specimen is a notched ball with an indent opposite to the notch. The recently developed “Notched Ball Test” produces a well defined and almost uniaxial stress field.The stress intensity factor of the crack in the notched ball is determined with FE methods in a parametric study in the practical range of the notch geometries, crack shapes and other parameters. The results correlate well with established calculations based on the Newman-Raju model.The new test is regarded as a component test for bearing balls and offers new possibilities for material selection and characterisation. An experimental evaluation on several ceramic materials will be presented in a consecutive paper.     

Computational Study for Protein-Protein Docking Using Global Optimization and Empirical Potentials

Protein-protein interactions are important for biochemical processes in biological systems. The 3D structure of the macromolecular complex resulting from the protein-protein association is a very useful source to understand its specific functions. This work focuses on computational study for protein-protein docking, where the individually crystallized structures of interacting proteins are treated as rigid, and the conformational space generated by the two interacting proteins is explored extensively. The energy function consists of intermolecular electrostatic potential, desolvation free energy represented by empirical contact potential, and simple repulsive energy terms. The conformational space is six dimensional, represented by translational vectors and rotational angles formed between two interacting proteins. The conformational sampling is carried out by the search algorithms such as simulated annealing (SA), conformational space annealing (CSA), and CSA combined with SA simulations (combined CSA/SA). Benchmark tests are performed on a set of 18 protein-protein complexes selected from various protein families to examine feasibility of these search methods coupled with the energy function above for protein docking study.     

A study of dilatation and acoustic propagation in solidifying fats and oils: I. Theoretical

A theoretical relationship is presented relating acoustic velocity to dilatation in two-phase systems. The theory is based on studies of seismic propagation by Kuster and Toksöz, who include acoustic propagation in a fluid matrix containing spherical or spheroidal solid inclusions as a special case of their theory. The relationship presented in this paper applies in the long wavelength limit and predicts a linear relationship between acoustic dilatation and volume dilatation in crystallizing liquids, when the acoustic dilatation is much less than unity. I anticipate that this theory may lead to the application of acoustics in the assessment of a wide range of crystallizing systems such as oils.     

塔板液相三维流场的研究（I）试验测量

本文针对热膜流速仪元件的工作原理提出了在平面旋转测量液体三维流速的方法,并测量了大型精馏塔板液相单相三维流场。为计算流体力学对塔板模拟提供了实验验证。测量结果发现在塔板的回流区、出口堰和塔壁附近流速的垂直分量是不可忽略的,有的地方流速的垂直分量的大小与其水平分量数量级相同。     

A Computational Study on Substituted and Unsubstituted Mono and Diazaanthracenes

Substituted (F, Cl, OH, and NO₂ ) diazaanthracene derivatives have been considered theoretically to obtain information about their stabilities and aromaticities. The expected decrease of aromaticity of parent anthracene by mono or diaza substitution has been compensated by substitution of one of the hydrogens of the system by an electronegative atom. The position of the substituent has been proved to be strongly effective on the aromaticity of the structure such that, the aromaticity is enhanced when the susbtituent is closer to the aza points.     

基于稳健优化的注塑件变形预补偿方法研究

针对凭经验进行预补偿设计容易造成预补偿失败的问题,提出了基于稳健优化的注塑件变形预补偿方法,综合考虑了塑料物性参数、浇注系统、冷却系统及工艺参数对注塑件翘曲变形量的影响,使变形预补偿更具有针对性。首先给出注塑件变形预补偿的原理,并提出利用模流分析来获得变形预补偿的数据,给出了MPI中实现预补偿的方法;接着提出了基于稳健优化的变形预补偿方法及实现流程,建立了适合变形预补偿的稳健优化模型;最后通过实例验证了提出的方法具有较好的可行性及工程实际应用价值。     

间位芳纶低线密度纺纱技术的工艺优化研究

根据间位芳纶的物理和力学性能特点,利用棉纺设备并分别对开清棉、梳棉、并条、粗纱、细纱、管纱、络筒等工序作出相应的工艺调整,以各工序工艺技术的优化适应间位芳纶低线密度纺纱,提出了生产高品质间位芳纶低线密度纱的可行性工艺路线。     

Structural and Photophysical Properties of a Cd(II) Coordination Polymer Based on Mixed Aromatic Ligands: A Combined Experimental and Theoretical Study

A novel one-dimensional Cd(II) coordination polymer (CP) based on mixed aromatic ligands was synthesized and characterized by X-ray diffraction, thermogravimetric analysis and spectroscopic analyses. Fingerprint plots in Hirshfeld surface analysis illustrate that the one-dimensional crystal structure of the CP is stabilized by C–H···O, π···π, C–H···π, and H···H intermolecular interactions. The structural and photophysical properties of the CP were then investigated by time-dependent density functional theory methods, and computational results well reproduced the experimental data. The combined investigations found a ligand-to-ligand charge transfer character during the electrons relax from the first singlet excited₁ state of the CP. The weak fluorescence of CP could be resulted from the energy interlacing of the frontier molecular orbitals (FMOs) of aromatic ligands and the fulfilled d ¹⁰ configuration of Cd(II). Herein, this CP exhibits as a potential tunable luminescent sensor by adjusting the energy levels of the FMOs of aromatic ligands.     

A Comparative Study of Polyamide and PMMA Denture Base Biomaterials: I. Thermal,Mechanical, and Dynamic Mechanical Properties

The fracture of denture base materials usually occurs due to accidental dropping and mishandling of these materials. Repeated fracture of denture base materials could be a problem for denture materials made of acrylic resins due to lack of toughness of PMMA-based denture materials. Use of a material with higher toughness might eliminate this problem. Properties of heat-polymerized poly(methyl methacrylate) (PMMA) and high-impact polyamide denture base biomaterials were compared. The test results showed that polyamide samples were more resilient and tougher. Polyamide biomaterials might be good candidate as an alternative to denture base PMMA materials for clinical situations of repeated fractures.     

Theoretical Study on Pyrolysis and Sensitivity of Energetic Compounds. Part I: Simple model molecules containing NO2 Group

UHF (Unrestricted Hartree-Fock) Molecular Orbital calculations have been first performed for studying the pyrolysis mechanism of five compounds (nitromethane, methyl nitrate, nitroamine, methyl nitroamine and dimethyl nitroamine) containing NO₂ group as the simple models of organic explosives by using PM3 and AM1 methods. The potential energy curves and activation energies of the five pyrolysis reactions (into radicals) have been obtained. The activation energies are consistent with the experimental impact sensitivity of these three kinds of explosives: C-nitro < N-nitro < O-nitro compounds. It is found that there is a parallel linear relationship between the bond orders of N NO₂ bond in the molecules of three nitroamine compounds and the activation energies of their initiation reactions breaking N NO₂ bond. The obtained correlation coefficients between bond orders and activation energies from PM3 and AM1 calculations are 0.9962 and 0.9999, respectively.