Peloton phase oscillations

A peloton may be defined as two or more cyclists riding in sufficiently close proximity to be located either in one of two basic positions: (1) behind cyclists in zones of reduced air pressure, referred to as ‘drafting’, or (2) in non-drafting positions where air pressure is highest. Cyclists in drafting zones expend less energy than in front positions. Qualitative observations of pelotons indicate oscillations between two primary phases. The first is a high density, low speed/power output phase. The second is a synchronized, low density, high speed or power output phase. Pelotons are observed to oscillate between phases, and mixed phases occur. Principles determining the first phase are coupling due to the energy savings of drafting, collision avoidance, and continuous passing. Principles determining the synchronized phase are similar, except that minimal passing is observed in this phase as cyclists approach maximum sustainable outputs. Phases self-organize as cyclists proceed through output thresholds, while strategic and tactical considerations are secondary. A computational simulation with an algorithm combining a coupling ratio, passing time, and constraints on angles of alignment, separation and cohesion (flocking rules), demonstrates phase oscillations.     

Efficient silver nanocluster photocatalyst for simultaneous methyl orange/4-chlorophenol oxidation and Cr(VI) reduction

Metal nanoclusters have shown great potential in photocatalysis, while simultaneous removal of both inorganic and organic contaminants by metal nanoclusters under visible light is less explored. Here, we synthesized Ag_m(SR)_n (SR represents 3-mercaptopropyltriethoxysilane ligand) nanoclusters (∼1 nm) via a reduction of silver triphenylphosphine under ambient conditions in the presence of 3-mercaptopropyltriethoxysilane. The nanocluster was characterized by UV–vis spectroscopy, high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectrum (FTIR), and X-ray photoelectron spectroscopy (XPS). Under 5 W blue LED, the Ag_m(SR)_n/P25 exhibits enhanced catalytic activity for simultaneous methyl orange (MO) oxidation and Cr(VI) reduction, and also for synchronous 4-chlorophenol oxidation and Cr(VI) reduction. Mechanism studies by electrochemical impedance spectroscopy (EIS), photoluminescence (PL), electron spin resonance (ESR) etc. and control experiments reveal that the unique structure of silver nanoclusters with thiolate ligands is vital to the high catalytic performance, and both the photo-generated holes and superoxide radicals are responsible for the decomposition of MO.     

Optimization for field emission from carbon nanotubes array by Fowler–Nordheim equation

In order to optimize the field emission from carbon nanotubes (CNTs) array by the emission current density, the calculation of the field emission was extended with the floating sphere model and the Fowler–Nordheim equation, and the trend of the emission current density versus the intertube distance (the distance between the nearest CNTs) was mainly discussed in this paper. Only considering the field enhancement factor in the previous works, the field emission from CNTs array was optimized only by possibly decreasing the intertube distance with the maximal field enhancement factor. Herein, both the field enhancement factor and the emission current density were taken into account, the field emission from CNTs array could be optimized analytically with the intertube distance of 10th of the tube height, which was much smaller than the estimated value and the experiment result.     

A novel 58-nuclei silver nanowheel encapsulating a subvalent Ag64+ kernel

The combination of CrO_4~(2-)anion and N,N′-dimethylformamide(DMF)-containing solvent helps to stabilize an atom-precise ultrasmall Ag_6 kernel into a 52-nuclei silver shell, giving a core-shell Ag_6@Ag_(52) wheel-like structure(SD/Ag58b). The solution behavior and photocurrent response property were investigated in details.     

Oxygen reduction at silver monolayer islands deposited on gold substrate

Underpotential deposition (UPD) of Ag on an Au(1 1 1) coated with a self-assembled monolayer (SAM) of decanethiol gives Ag islands having monatomic height. After reductive desorption of the SAM, Ag monolayer islands were exposed and their catalytic activities for oxygen reduction were examined by voltammetry and hanging meniscus rotating disk (HMRD) measurements. Comparison of electrochemical properties and STM images of electrodes revealed that an island with less than 750 Ag-atoms showed two-electron reduction and that an island with over than 4000 Ag-atoms is necessary to show the original ability of four-electron reduction.     

Ultrasound-driven titanium modification with formation of titania based nanofoam surfaces

Titanium has been widely used as biomaterial for various medical applications because of its mechanical strength and inertness. This on the other hand makes it difficult to structure it. Nanostructuring can improve its performance for advanced applications such as implantation and lab-on-chip systems. In this study we show that a titania nanofoam on titanium can be formed under high intensity ultrasound (HIUS) treatment in alkaline solution. The physicochemical properties and morphology of the titania nanofoam are investigated in order to find optimal preparation conditions for producing surfaces with high wettability for cell culture studies and drug delivery applications. AFM and contact angle measurements reveal, that surface roughness and wettability of the surfaces depend nonmonotonously on ultrasound intensity and duration of treatment, indicating a competition between HIUS induced roughening and smoothening mechanisms. We finally demonstrate that superhydrophilic bio-and cytocompatible surfaces can be fabricated with short time ultrasonic treatment.     

纳米铝化合物与生物有机分子界面作用的研究进展

本文概述了环境和生物体系中纳米铝化合物的存在形态,主要介绍了无机纳米形态铝化合物与生物有机分子的表面/界面的作用以及宏观、微观和计算机模拟等研究方法,展望了该领域研究的最新进展。     

Spontaneous oscillations in gold electrodeposition

We report the appearance of spontaneous oscillations during the electrodeposition of gold along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium monolayer, when a current ramp with a rate comprised between 1 and 1.5 nA s⁻¹ is applied to the working electrode. Alternating sequences of two-dimensional (2D) growth and three-dimensional (3D) thickening of the deposits leading to gold films with a well-defined terraced structure are observed. Such a phenomenon appears to be produced by the competition between two mechanisms controlling the current density J₁: one is the current ramp which tends to increase J₁ and the other one is the growing of the gold deposit which induces a decrease of J₁.     

Coordination compounds of 1,4-dihydroxybenzoquinone and its homologues. Structures and properties

Metal complexes of 1,4-dihydroxy-benzoquinone and its homologues (H₂C₆X₂O₄) are reviewed, focusing on assembled structures based on their X-ray crystallographic structures reported so far. A wide variety of crystal structures based on mononuclear, binuclear, polynuclear complexes and extended structures of coordination polymers or hydrogen bond linked networks are listed in relation to the coordination modes such as the monodentate, bidentate, and bis-bidentate form of the ligands. Their physico-chemical properties such as redox, UV–vis, EPR and magnetic properties are described. The ligand, H₂C₆X₂O₄, discussed here is one of the most useful multifunctional ligands, affording not only various self-assembled frameworks via coordination, hydrogen, and coulomb linkages, but also unique electronic structures, which are accompanied by charged and spin states. Their characteristics are mentioned in detail.     

Interfacial charge transfer in carbon nitride heterojunctions monitored by optical methods

Solar energy conversion is inciting tremendous research efforts in many fields due to the vast potential of sunlight as a sustainable energy source. For solar energy to become widely used and become a major component of our energy mix, energy storage on large scales must be addressed and the components used must be abundant. Artificial photosynthesis to produce solar fuels holds promise as a way to convert solar energy into storable energy. Organic photocatalysts have rapidly established themselves as a viable alternative to inorganic systems. Organic photocatalyst can be prepared from inexpensive precursors and offer a synthetic versatility and tunability that can be exploited to improve efficiencies. Carbon nitride (CN_x) has emerged as a leading organic photocatalyst with advantageous chemical and photo stabilities. Recombination of photogenerated electrons and holes limit the efficiency of CN_x materials below levels necessary to become a viable energy production system. To improve the efficiency and key characteristics such as light harvesting, charge carrier lifetime, and interfacial rate of charge transfer, a second material is put in contact with CN_x to form a heterojunction. While there are many examples of heterojunctions improving the photocatalytic activity beyond that of the isolated CN_x, we are still lacking the deep understanding of charge carrier dynamics necessary to rationalize the improvements and design optimal junctions. This review covers the studies of CN_x heterojunctions that have used optical methods to monitor the charge carrier dynamics. Time-resolved photoluminescence (TRPL) is the most common technique used and there are many examples that have used transient absorption spectroscopy (TAS) to probe the charge carrier dynamics. However, attempting to link the lifetime change to the activity differences does not yield a clear trend. It is likely that the reactive charges are not consistently being monitored and is obscuring the expected correlations. Both shorter and longer charge carrier lifetimes can be observed with both TRPL and TAS techniques and can be interpreted as arising from interfacial charge separation. Even when the same materials are used in the junction there is no consistency in observing a shorter or longer lifetime. The holistic view of charge carrier dynamics in CN_x heterojunctions presented here intends to identify overarching themes from a wide range of CN_x-containing systems and help take stock of where our current understanding stands. More specific spectral assignments and linking the observed lifetimes to certain photophysical or photochemical processes are needed to build models to help us understand the links between the charge carrier dynamics and the activity. These are crucial to develop general strategies that will lead to optimal CN_x heterojunctions.