Dynamically modulated synthesis of hollow metal-organic frameworks for selective hydrogenation reactions

Hollow metal-organic frameworks(MOFs)have attracted increasing attention in the field of catalysis in recent years due to their unique cavity structure with fast mass-diffusion rates and easily accessible active sites.Here,we report the use of dynamic modulators,which are formed by the in-situ imine condensation reaction of 4-aminobenzoic acid and 4-formylbenzoic acid,to regulate the growth of MOFs to synthesize well-defined hollow thioether functionalized UiO-67(denoted as H-UiO-67-S)single crystals.After supporting Pd nanoparticles,the designed catalysts Pd@H-UiO-67-S show excellent conversion(>99.9%),selectivity(>99.9%),and stability(10 cycles)in the selective hydrogenation of nitrobenzenes with other reducible groups.Density functional theory calculations and the experimental results reveal that Pd nanoparticles not only selectively adsorb the nitro-groups on nitrobenzene,but also restrict the adsorption of the aniline product,due to the interaction of thioether with Pd in the confined pores of H-UiO-67-S,finally result in a significant increase in selectivity of nitro-hydrogenation.

An Improved CFD-synthesis Method for Predicting Inlet Dynamic Distortion

This article presents an improved computational fluid dynamics （CFD）-synthesis method to predict dynamic distortion. A steady-state flow field is derived from a CFD solution, through which are acquired total pressure, density, turbulence kinetic energy and others in steady-state at an aerodynamic interface plane （AIP）. Back-propagation artificial neural network （BP ANN） is used to find out the relationship between the measured flight turbulence and the CFD-computed turbulence parameters. The dynamic pressure is obtained by incorporating CFD-found total steady-state pressure with fluctuating pressure. Finally, the dynamic distortion is predicted by means of the synthesized dynamic pressure. The fairly good agreement between the computed inlet surface pressure and the flight test data bears out the reliability of CFD solution used in this article. To validate the proposed method, six sets of flight test data are used and the results show that the predicted dynamic distortion is well in line with the distortion displayed in flight tests. An examination of the traditional method is also accomplished and the comparison also shows that the proposed method is superior to the traditional one in higher consistency with flight test data.

Scalable Ambient Pressure Synthesis of Covalent Organic Frameworks and Their Colorimetric Nanocomposites through Dynamic Imine Exchange Reactions

A novel scale-up ambient pressure synthetic strategy for the preparation of imine-based covalent organic frameworks（COFs） was proposed through dynamic imine exchange reaction mechanism. The obtained COFs exhibited good crystallinity and much higher porosity comparable to their solvothermally synthesized counterparts. Moreover, under ambient pressure, the COF nanofibers could readily grow on the surface of polyimide films, and the resulted nanocomposite film showed an interesting colorimetric acid-responsive behavior.

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDY FOR COMBUSTION SYNTHESIS OF TITANIA NANOPARTICLES

Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Com-putations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the op-timal reaction temperature, the suitable mole ratio of oxygen to titanium tetrachloride, and the best inlet positions of tita-nium tetrachloride. The mean particle diameter was obtained from particle-dynamic simulation. A combustion apparatus was setup to synthesize titania nanoparticles by the oxidation and hydrolysis of titanium tetrachloride at high tempera-tures. Experimental investigation verified some results obtained from thermodynamic and particle-dynamic computations.

An efficient formulation based on the Lagrangian method for contact–impact analysis of flexible multi-body system

In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body systems.Generally,the penalty method and the Hertz contact law are the most commonly used methods in engineering applications.However,these methods are highly dependent on various non-physical parameters,which have great effects on the simulation results.Moreover,a tremendous number of degrees of freedom in the contact–impact problems will influenc thenumericalefficien ysignificantl.Withtheconsideration of these two problems,a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact–impact problems in fl xible multi-body system numerically.Meanwhile,the finit element meshing laws of the contact bodies will be studied preliminarily.A numerical example with experimental verificatio will certify the reliability of the presented formulationincontact–impactanalysis.Furthermore,aseries of numerical investigations explain how great the influenc of the finit element meshing has on the simulation results.Finally the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficien y.

ELECTRON MICROSCOPIC AUTORADIOGRAPHIC STUDIES ON DYNAMICS AND LOCATION OF DNA SYNTHESIS OF DUCK PLAGUE VIRUS

Electron microscopic autoradiographic studies on the dynamics and location of DNAsynthesis by means of incorporation of ~8H-thymidine during the replication of duck plaguevirus (DPV) revealed that the duration of DNA synthesis of DPV was rather long. The repli-cation of viral DNA occurred simultaneously with the assembly procedure of nucleocapsids, thematuration and release of viruses. DNA synthesis of DPV occurred in the matrix with lowerelectron density in the nucleus. The replicated viral DNA accumulated in the viroplast With highelectron density where the assembly of nucleocapsids occurred. The viroplast with high electrondensity was not the region of viral DNA synthesis.

A Single-legged Robot Inspired by the Jumping Mechanism of Click Beetles and Its Hopping Dynamics Analysis

The click beetle can jump up with a hinge when it is on the dorsal side.This jumping mechanism is simple and suitable as an inspiration for designing a simple,small,and reliable hopping robot.We report a single-legged robot inspired by the jumping mechanism of click beetles.It is 85 mm high,60 mm long,and 41 mm wide,and weighs about 49 g.The robot has good hopping performance that the hopping height is about 4 times-4.3 times of its body height.It is capable for rescue missions that require to enter enclosed spaces through cracks and narrow channels.In addition,hopping dynamics of the robot is important to understand its jumping mechanism and improve the robot’s hopping performance.But existing dynamic study does not complete the analysis including all stages in the hopping which are pre-hopping,take-off,and air-flying.We propose the decomposition method to study dynamics of the three stages separately,and synthesize them with related parameters.The dynamic synthesis of multi-motion states in a hopping cycle of the single-legged hopping robot is implemented.The hopping performance and dynamic synthesis theory of the robot are verified by simulations and experiments.Our study helps lay the foundation for design and hopping control of simple hopping robot systems.

FORMATION OF MICRO-POROUS SPHERICAL PARTICLES OF CALCIUM SILICATE(XONOTLITE) IN DYNAMIC HYDROTHERMAL PROCESS

Stirring during hydrothermal synthesis plays an important role in the formation of porous spherical xonotlite particles. The size of spherical particles formed during dynamic hydrothermal process is related to the size of minimum vortices in the reaction slurry, which is determined by stirring speed. The kinetics of growth of xonotlite particles is de-termined by measuring the apparent viscosity of the reactant slurry at various reaction time and reaction temperatures. It is found that the growth of particles follows the contracting-volume equation, and the activation energies for nucleation and growth are 104 and 123 kJ.mol-1, respectively.

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production （〉1,000 T-year-1） of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics （CFD） calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor.