Contact line motion in confined liquid-gas systems: Slip versus phase transition

In two-phase flows, the interface intervening between the two fluid phases intersects the solid wall at the contact line. A classical problem in continuum fluid mechanics is the incompatibility between the moving contact line and the no-slip boundary condition, as the latter leads to a nonintegrable stress singularity. Recently, various diffuse-interface models have been proposed to explain the contact line motion using mechanisms missing from the sharp-interface treatments in fluid mechanics. In one-component two-phase (liquid-gas) systems, the contact line can move through the mass transport across the interface while in two-component (binary) fluids, the contact line can move through diffusive transport across the interface. While these mechanisms alone suffice to remove the stress singularity, the role of fluid slip at solid surface needs to be taken into account as well. In this paper, we apply the diffuse-interface modeling to the study of contact line motion in one-component liquid-gas systems, with the fluid slip fully taken into account. The dynamic van der Waals theory has been presented for one-component fluids, capable of describing the two-phase hydrodynamics involving the liquid-gas transition [A. Onuki, Phys. Rev. E 75, 036304 (2007)]. This theory assumes the local equilibrium condition at the solid surface for density and also the no-slip boundary condition for velocity. We use its hydrodynamic equations to describe the continuum hydrodynamics in the bulk region and derive the more general boundary conditions by introducing additional dissipative processes at the fluid-solid interface. The positive definiteness of entropy production rate is the guiding principle of our derivation. Numerical simulations based on a finite-difference algorithm have been carried out to investigate the dynamic effects of the newly derived boundary conditions, showing that the contact line can move through both phase transition and slip, with their relative contributions determined by a competition between the two coexisting mechanisms in terms of entropy production. At temperatures very close to the critical temperature, the phase transition is the dominant mechanism, for the liquid-gas interface is wide and the density ratio is close to 1. At low temperatures, the slip effect shows up as the slip length is gradually increased. The observed competition can be interpreted by the Onsager principle of minimum entropy production.     

First-principles study of hydrogen adsorption in metal-doped COF-10

Covalent organic frameworks (COFs), due to their low-density, high-porosity, and high-stability, have promising applications in gas storage. In this study we have explored the potential of COFs doped with Li and Ca metal atoms for storing hydrogen under ambient thermodynamic conditions. Using density functional theory we have performed detailed calculations of the sites Li and Ca atoms occupy in COF-10 and their interaction with hydrogen molecules. The binding energy of Li atom on COF-10 substrate is found to be about 1.0 eV and each Li atom can adsorb up to three H(2) molecules. However, at high concentration, Li atoms cluster and, consequently, their hydrogen storage capacity is reduced due to steric hindrance between H(2) molecules. On the other hand, due to charge transfer from Li to the substrate, O sites provide additional enhancement for hydrogen adsorption. With increasing concentration of doped metal atoms, the COF-10 substrate provides an additional platform for storing hydrogen. Similar conclusions are reached for Ca doped COF-10.     

Short and straightforward total synthesis of Ammosamide B

A simple and five steps total synthesis of Ammosamide B has been developed. The tricyclic pyrroloquinoline in Ammosamides was constructed in one step based on Doebner-Miller reaction between 1,3-diamine-4,6-dinitrobenzene 8 and dimethyl-2-oxo glutaconate 9.     

Heterobimetallic complexes of lanthanide and lithium metals with dianionic guanidinate ligands: Syntheses, structures and catalytic activity for amidation of aldehydes with amines

Reactions of triguanidinate lanthanide complexes Ln[(ⁱPrN)(NC₆H₄p-Cl)C(NHⁱPr)]₃ (Ln = Nd, Y) with 3 equiv. of n-BuLi gave [Li(THF)(DME)]₃Ln[μ-η²η¹ (ⁱPrN)₂C(NC₆H₄p-Cl)]₃, which represents the first structurally characterized complexes of lanthanide and lithium metals with dianionic guanidinate ligands. The Nd complex was found to be an effective catalyst for amidation of aldehydes with amines under mild conditions with a wide scope of substrates.     

Experimental Study of Capacitive RF <Emphasis Type="Italic">c</Emphasis>-C<Subscript>4</Subscript>F<Subscript>8</Subscript> Discharge with Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Capacitive radio frequency (RF) discharge of c-C₄F₈ (octafluorocyclobutane) has been studied with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS) at 4 Torr and 33.33 kHz. Various free radicals and reactive intermediates have been identified through measurement of photoionization mass spectra and photoionization efficiency (PIE) spectra. CF₂=CF₂ is main product in the plasma, indicating that the dissociation of c-C₄F₈ into CF₂=CF₂ is one of prominent reactions in the present experimental conditions. The observation of large species including C₅F₈, C₅F₁₀ and C₆F₁₀ is presented in our work. Besides, the dependences of the signals of neutral species in the discharge of c-C₄F₈ on RF power are presented in this paper.     

Lanthanide/zinc centered photoactive hybrids with functional sulfonamide linkage: Coordination bonding assembly,characterization and photophysical properties

In this paper, two novel kinds of organic–inorganic monomer, SUA-APEMS and SUA-APS, have been achieved by modifying 5-sulfosalicylic acid (SUA) with 3-aminopropyl-methyl-diethoxylsilane (APEMS) and 3-aminopropyl trimethoxysilane (APS). These two organic–inorganic monomers were used as multi-functional bridged components, which can coordinate to metal ions (Tb³⁺/Eu³⁺/Zn²⁺) with carbonyl groups, strongly absorb ultraviolet and effectively transfer energy to metal ions through their triplet excited state, as well as involve in the sol–gel process with inorganic host precursor tetraethoxysilane (TEOS), resulting two series of molecular hybrid materials (named as SUA-APEMS/APS-RE) with double chemical bond (RE(Zn)–O coordination bond and Si–O covalent bond). The effective intra-molecular energy transfer process gives rise to the characteristic emission of metal ions and the chemical bond make the hybrid materials owning better properties.     

无线光通信系统大气信道特性的分析研究

介绍了大气激光通信的基本原理、关键技术和应用领域;分析了大气信道对无线光通信系统的影响,着重分析大气的衰减效应和大气的湍流效应;指出在我国特定地区进行大气信道测试的必要性;最后介绍和分析了大气信道特性的主要测试方法.     

浅谈电网谐波

对电网中谐波大量涌现原因及出现干扰问题应采取的相关抑制措施。     

Luminescence properties of [Ru(bpy)2MDHIP]2+ modulated by the introduction of DNA,copper(II) ion and EDTA

The luminescence properties of [Ru(bpy)₂MDHIP]²⁺ (bpy = 2,2′-bipyridine, MDHIP = 2,4-dihydrophenyl-imidazo[4,5-f][1,10]phenanthroline) in the absence and presence of DNA modulated by the introduction of Cu²⁺ ion and EDTA have been investigated. It is found that the ruthenium(II) complex can insert and stack between the base pairs of calf thymus DNA with MDHIP ligand, and the intramolecular hydrogen bond is located inside of the DNA. The presence of DNA can enhance the luminescence intensities of [Ru(bpy)₂MDHIP]²⁺ both in buffer solution and on an ITO surface. Moreover, the luminescence intensities of [Ru(bpy)₂MDHIP]²⁺ and DNA-bound [Ru(bpy)₂MDHIP]²⁺ are quenched by Cu²⁺, and next recovered by the addition of EDTA. The repetitive luminescence-modulations have been achieved through the introduction of equimolar Cu²⁺ and EDTA, respectively. In addition, it becomes evident that the number of luminescence-modulation cycles for [Ru(bpy)₂MDHIP]²⁺ in the absence and presence of DNA is influenced by the cumulative concentrations of CuEDTA, generated successively by the strong coordination of Cu²⁺ to EDTA.     

Synthesis, structure and magnetic properties of two new azido-Co(II) coordination architectures: from ferromagnetic coupling to single-chain-magnets

Two new azido-Co(II) complexes with pyrazine carboxylato ligands, [Co(N(3))(L)·H(2)O](n) (L = pyrazine-2-carboxylato) (1) and [CoNa(N(3))(2)(L)](n) (2), have been obtained by carefully tuning the Co(II):N(3)(-) ratio. Here we present the structural and magnetic characterization of these new species. Modulation of the coordination environment of Co(II) leads to a variation of the magnetic properties of the obtained compounds. Complex 1 exhibits ferromagnetically coupled [Co(2)] units that form the rungs of the ladder with a nearly negligible coupling between these units, while complex 2 is a 2D arrangement of 1D Co(II) single-chain magnets.