"Micro-pottery"--marangoni effect driven assembly of amphiphilic fibers

We report spontaneous supra-assembly of fibrous surfactant crystallites at the air-solution interface resulting in spectacular arrays of two-dimensional spiral and three-dimensional "micro-pottery"-like superstructures. Surface pressure differential driven bending of the embryonic fiber nuclei and Marangoni convection driven fiber migration/alignment appear to be the causal factors behind this phenomenon. The assemblies form at specific crystal-growth velocities dictated by the relative time scales for fiber bending/alignment and their rigidification/immobilization as they grow. Although our studies are restricted to a specific class of amphiphiles, namely, alkaline metal salts of linear fatty acids, the phenomenon should be generic to amphiphilic molecules that crystallize into flexible fibers.     

Simulating the collapse transition of a two-dimensional semiflexible lattice polymer

It has been revealed by mean-field theories and computer simulations that the nature of the collapse transition of a polymer is influenced by its bending stiffness epsilon(b). In two dimensions, a recent analytical work demonstrated that the collapse transition of a partially directed lattice polymer is always first order as long as epsilon(b) is positive [H. Zhou et al., Phys. Rev. Lett. 97, 158302 (2006)]. Here we employ Monte Carlo simulation to investigate systematically the effect of bending stiffness on the static properties of a two-dimensional lattice polymer. The system's phase diagram at zero force is obtained. Depending on epsilon(b) and the temperature T, the polymer can be in one of the three phases: crystal, disordered globule, or swollen coil. The crystal-globule transition is discontinuous and the globule-coil transition is continuous. At moderate or high values of epsilon(b) the intermediate globular phase disappears and the polymer has only a discontinuous crystal-coil transition. When an external force is applied, the force-induced collapse transition will either be continuous or discontinuous, depending on whether the polymer is originally in the globular or the crystal phase at zero force. The simulation results also demonstrate an interesting scaling behavior of the polymer at the force-induced globule-coil transition.     

Ab initio calculations of the electronic states of AsH2 including dissociation characteristics

Multireference configuration interaction calculations have been carried out for low-lying electronic states of AsH(2). Bending potentials for the ten lowest states of AsH(2) are obtained in C(2v) symmetry for As-H distances fixed at the the ground state equilibrium value of 2.845 a(0), as well as for the minimum energy path constrained to R(1) = R(2). The calculated equilibrium geometries for the X?(2)B(1) ground state and the A?(2)A(1) excited state agree very well with the previous experimental and theoretical results, whereas the data for the higher-lying states are obtained for the first time. Asymmetric potential energy surface (PES) cuts (at R(1) = 2.845 a(0), θ = 90.7°) and two-dimensional (2D) PESs for the lowest three states are also new. The calculated ab initio data are used for analysis of possible AsH(2) photodissociation channels and predissociation effects. It is shown that the A?(2)A(1)-X?(2)B(1) transition dipole moment decreases with increasing bending angle, which influences the intensity distribution in the A?(0,0,0)→X? emission spectrum (v(2)' bending series), shifting its maximum to smaller v(2)' quantum numbers.     

Coincidence of the molecular organization of beta-substituted oligothiophenes in two-dimensional layers and three-dimensional crystals

The molecular arrangements of three different alkyl-substituted oligothiophenes both in two-dimensional adsorbed layers at a substrate interface and in bulk three-dimensional crystals were studied. Scanning tunneling microscopy (STM) was used to investigate the ordering of the conjugated oligomers in two-dimensional layers adsorbed on graphite. These data were compared with the X-ray structure determinations of single crystals revealing the arrangement in the three-dimensional bulk material. Quaterthiophenes 1 and 2, bearing dodecyl and hexyl side chains, respectively, exhibit a lamella-type stacking of the conjugated backbone concomitant with an interlocking of the alkyl side chains both on the surface and in the crystal. In contrast, the arrangement of propyl-substituted quaterthiophene 3 is rather "herringbone-like" due to the reduced interactions of the shorter alkyl side chains. In all three cases, evidently, the two-dimensional ordering at the graphite surface is coincident with the molecular packing in one cross-section of the three-dimensional crystal.     

Intramolecular vibrational energy redistribution in the highly excited fluoroform molecule: a quantum mechanical study using the multiconfiguration time-dependent Hartree algorithm

The present paper is devoted to a detailed study of the intramolecular vibrational energy redistribution in fluoroform initiated by a local mode excitation of the CH stretch [nnu(CH) (n=1,...,4)]. All nine internal degrees of freedom are explicitly taken into account and the full quantum mechanical simulation is performed by means of the multiconfiguration time-dependent Hartree algorithm. The existence of different time scales considerably complicates the dynamics. The mode-to-mode energy transfer is analyzed by calculating the evolution of the partial energies of all vibrational modes. This study emphasizes the crucial role played by the two-dimensional FCH bending modes which act as an energy reservoir. The fast energy flow into these bending modes significantly hinders an energy flow from the CH chromophore. Finally, our results are compared with those obtained previously with the wave operator sorting algorithm approach.     

Isoelectric Focusing with Immobilized pH Gradients

Abstract

The technique of isoelectric focusing (IEF) via immobilized pH gradients (IPG) was first announced to the scientific community at a meeting of the International Electrophoresis Society in Athens, April 1982, as the result of an intensive collaborative effort [1]. In five years, the technique has been extensively developed in three fundamental aspects: analytical, preparative and as a first dimension of two-dimensional (2-D) maps. The merits and, recently, the flaws of the IPG technique have been evaluated and recognized, so that at the present writing we feel it is ready for successful introduction in most life-science laboratories.     

A measure of folding complexity for d-dimensional polymers

A measure of folding characterizes aspects of the instantaneous organization of a polymer chain in space. For three-dimensional polymers (D = 3), one such measure is the mean overcrossing number. An intuitively similar property, the radial intersection number, has been proposed as a tool to characterize "folding features" in two-dimensional polymers (D = 2). In this work, we show rigorously that these measures are indeed related and that they can be derived as particular cases within a single, unified formulation. The present approach provides an analytical expression for a measure of folding complexity that can be applied to generic D-dimensional polymers. In the case D = 2, we show results for models derived from experimental structures by using optimized multidimensional scaling transformations for data compression.     

A proposal for a novel evaluation method of the bending velocities of polymer actuators

This paper proposes a novel evaluation method for three types of velocities of the bending processes of polymer actuators. These velocities are the initial, bending, and backtracking velocities, and the method considers three processes of the bending motion. By calculating the time–width differentiation of the displacement of each process, the initial, bending, and backtracking velocities can be evaluated. Δt of 0.1, 1.0, and 10.0 s were considered to be the differentiations of bending displacement, and the initial, bending, and backtracking velocities were calculated to be 2.15, 0.46, and 0.002 mm/s, respectively. By using the method proposed here, we found that the initial velocity at 75%RH is 2.5 times faster than it was at 45%RH by increasing the adsorption of water. Copyright © 2013 John Wiley & Sons, Ltd.     

二维相关荧光光谱技术

从发展历史、计算方程、一般规则和特有性质等方面系统地介绍了近年来在二维相关荧光光谱技术方面的方法探索和应用进展。以不同的外扰方式,如浓度、激发波长、猝灭以及其他如pH等分类,举例阐述了二维荧光相关光谱的可操作性及其应用,并与普通一维荧光光谱比较,说明了二维荧光相关光谱技术的优势。     

Apolipoprotein E and other cerebrospinal fluid proteins differentiate ante mortem variant Creutzfeldt-Jakob disease from ante mortem sporadic Creutzfeldt-Jakob disease

The ability to perform an ante mortem differential diagnosis of Creutzfeld-Jakob disease (CJD) is aided by several clinical and molecular tests. There is a need for molecular tests which can reliably distinguish ante mortem variant CJD (vCJD) from ante mortem sporadic CJD (spCJD). A proteomics approach employing two-dimensional protein electrophoresis is applied to the study of ante mortem CSF samples obtained in collaboration with the CJD Surveillance Unit and the National Hospital for Neurology and Neurosurgery. The sample set includes two cases of vCJD, three cases of spCJD and three neurologic controls. Preliminary data using a panel of seven molecular markers is able to distinguish vCJD from spCJD using a heuristic clustering algorithm. One of the molecular markers has been identified as apolipoprotein E which appears to be upregulated in the cerebrospiral fluid (CSF) of patients with vCJD as compared to spCJD. Analysis of ante mortem CSF may help to differentiate patients with vCJD from those patients with spCJD.     

General theory of deformation of viscoelastic substances

The general theory of the deformation of viscoelastic substances developed in two previous papers for the one-dimensional case is now extended to three dimensions. The integro-differential equations obtained are generalizations of the well-known Navier-Cauchy equations and, like these, only apply to small deformations. Some special cases are considered in detail and lead to interesting conclusions. In particular, the theory predicts that for incompressible high polymers, one should obtain the same creep and relaxation functions when the material is subjected to extension, torsion, or bending.     

MXenes及MXenes复合材料的制备及其在能量存储与转换中的应用

综述了新型过渡金属碳化物和/或氮化物(MXenes)二维纳米材料的合成及其在电化学能源存储与转换中应用的研究进展,这些应用可以分为如下三类:二次电池、超级电容器以及电化学催化。 由于具有二维结构、金属导电性、亲水性表面以及其它优点,MXene二维纳米材料在这些应用领域展示了良好的性能,而且还可以通过嵌入、复合、掺杂、组装等方法来进一步提高其电化学性能。 本文为新型MXenes以及相关材料的开发、合成和应用提供了思路,这种新型MXenes 材料可以用于能量存储与转换、电子和催化等领域。     

Analysis of a reversible five-point bending configuration based on a novel two-sense support

A novel two-sense support for flexural tests has been designed and manufactured in Ikerlan. The aim of this support is to do two-sense bending fatigue tests. In order to reduce the displacement corresponding to a given stress, a novel test configuration, designated as five-point bending, is modelled analytically. Basically, it is a three-point configuration with two supports at the ends that exert forces in the same sense as the applied load. In this way, a partial clamping is obtained that can be modelled by concentrated loads. The model has been checked carrying out quasi-static three-point and five-point bending tests at different spans in unidirectional carbon/epoxy composite specimens. Flexural modulus and the out-of-plane shear modulus have been obtained by linear regression in both cases, after having obtained experimentally the stiffness of the system.     

Robust Proton Conduction against Mechanical Stress in Flexible Free-Standing Membrane Composed of Two-Dimensional Coordination Polymer

Introduction of mechanical flexibility into proton-conducting coordination polymers (CPs) is in high demand for future protonic applications such as fuel cells and hydrogen sensors. Although such mechanical properties have been primarily investigated in one-dimensional (1D) CPs, in this study, we successfully fabricated highly flexible free-standing CP membranes with a high surface-to-volume ratio, which is beneficial for enhanced performance in the aforementioned applications. We fabricated a layered CP, Cu₂(NiTCPP) (H₄(H₂TCPP); 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin), in which a two-dimensional (2D) square grid sheet composed of tetradentate nickel porphyrins and paddlewheel-type copper dimers was connected to each other by weak van der Waals forces. The mechanical flexibility was evaluated by bending and tensile tests. The flexural and Young's moduli of the membrane were significantly higher than those of conventional Nafion membranes. Electrochemical impedance spectroscopy analysis revealed that the in-plane proton conductivity of the membrane was maintained even under applied bending stress. Because the X-ray diffraction analysis indicates that the proton-conducting pathway through the hydrogen bonding network remains intact during the bending operation, our present study provides a promising strategy for the fabrication of new and advanced 2D CPs without using substrates or additional polymers for protonic devices.     

Evaporation of ethanol and ethanol-water mixtures studied by time-resolved infrared spectroscopy

The knowledge of the physics and the chemistry behind the evaporation of solvents is very important for the development of several technologies, especially in the fabrication of thin films from liquid phase and the organization of nanostructures by evaporation-induced self-assembly. Ethanol, in particular, is one of the most common solvents in sol-gel and evaporation-induced self-assembly processing of thin films, and a detailed understanding of its role during these processes is of fundamental importance. Rapid scan time-resolved infrared spectroscopy has been applied to study in situ the evaporation of ethanol and ethanol-water droplets on a ZnSe substrate. Whereas the evaporation rate of ethanol remains constant during the process, water is adsorbed by the ethanol droplet from the external environment and evaporates in three stages that are characterized by different evaporation rates. The adsorption and evaporation process of water in an ethanol droplet has been observed to follow a complex behavior: due to this reason, it has been analyzed by two-dimensional infrared correlation. Three different components in the water bending band have been resolved.     

氧化石墨烯和石墨烯在催化领域中的应用研究进展

石墨烯具有独特的二维平面结构,其导电性能好,比表面积大,耐酸碱,耐高温.基于石墨烯的优异特性,本文作者从材料的合成和结构等方面对石墨烯基催化剂的研制及其催化性能进行了评述.介绍了石墨烯催化体系的类型和机理,对石墨烯催化中存在的问题进行了简单分析,并对石墨烯在催化领域的应用前景进行了展望.     

Experimental and theoretical study of the photodissociation of bromo-3-fluorobenzene

The UV photodissociation of bromo-3-fluorobenzene under collisionless conditions has been studied as a function of the excitation wavelength between 255 and 265 nm. The experiments were performed using ultrafast pump-probe laser spectroscopy. To aid in the interpretation of the results, it was necessary to extend the theoretical framework substantially compared to previous studies, to also include quantum dynamical simulations employing a two-dimensional nuclear Hamiltonian. The nonadiabatic potential energy surfaces (PES) were parameterized against high-level MS-CASTP2 quantum chemical calculations, using both the C-Br distance and the out-of-plane bending of the bromine as nuclear parameters. We show that the wavelength dependence of the photodissociation via the S0-->1pipi*-->1pisigma* channel, accessible with a approximately 260 nm pulse, is captured in this model. We thereby present the first correlation between experiments and theory within the quantitative regime.     

A volume-amending method to improve mass conservation of level set approach for incompressible two-phase flows

A volume-amending method is developed both to keep the level set function as an algebraic distance function and to preserve the bubble mass in a level set approach for incompressible two-phase flows with the significantly deformed free interface. After the traditional reinitialization procedure, a vol-ume-amending method is added for correcting the position of the interface according to mass loss/gain error until the mass error falls in the allowable range designated in advance. The level set approach with this volume-amending method incorporated has been validated by three test cases: the motion of a single axisymmetrical bubble or drop in liquid, the motion of a two-dimensional water drop falling through the air into a water pool, and the interactional motion of two buoyancy-driven three- dimensional deformable bubbles. The computational results with this volume-amending method in-corporated are in good agreement with the reported experimental data and the mass is well preserved in all cases.     

Chemistry of and on TiO2-anatase surfaces by DFT calculations: a partial review

We review recent theoretical studies of the surfaces and interfaces of the anatase polymorph of TiO₂. We discuss aspects of the surface structure, stability, and reactivity, as well as the growth and stability of anatase-supported oxide nanostructures of catalytic interest. Finally, we report on recent investigations of two-dimensional titania systems which appear to be closely related to anatase and which may have an important role during the growth of anatase nanoparticles.     

Theoretical studies of ion neutralization: Two-dimensional tight binding models

The neutralization of ions impinging on a substrate is modeled by treating the substrate as both a two-dimensional, tight-binding, semi-infinite sheet and a two-dimensional, tight-binding, infinite sheet. In both cases the equations of motion are set up in a generalized Langevin format. Results are presented for a model interaction and compared with previous computations using a semi-infinite chain model and an infinite chain model.