Polarized recombination of acoustically transported carriers in GaAs nanowires

ABSTRACT: : The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport.     

水性涂料涂膜泛黄的评价方法及其影响因素的探讨（Ⅱ）

4 纯丙烯酸酯乳胶树脂与苯乙烯丙烯酸酯 乳胶树脂在涂料泛黄上的差别 　　室外涂料的泛黄已成为涂料工业中争论激烈的一个问题,对此有许多观点。观点之一是：以苯乙烯丙烯酸酯乳胶树脂为基料的室外涂料比以纯丙烯酸酯乳胶树脂为基料的室外涂料更容易泛黄。普遍观点是：室外涂料的泛黄程度与苯乙烯丙烯酸酯乳胶（分散体）中的苯乙烯含量有关。实际上,聚合物膜的耐久性（以及以聚合物为基料的涂料的耐久性）不仅仅与单体选择（苯乙烯含量）有关,还有下列因素的作用： 　　●聚合物中的杂质和添加剂; 　　●单体的排序; 　　●聚合物结构…     

Decoding the Chemical Language of Motile Bacteria by Using High‐Throughput Microfluidic Assays

Motile bacteria navigate chemical environments by using chemoreceptors. The output of these protein sensors is linked to motility machinery and enables bacteria to follow chemical gradients. Understanding the chemical specificity of different families of chemoreceptors is essential for predicting and controlling bacterial behavior in ecological niches, including symbiotic and pathogenic interactions with plants and mammals. The identification of chemical(s) recognized by specific families of receptors is limited by the low throughput and complexity of chemotaxis assays. To address this challenge, we developed a microfluidic‐based chemotaxis assay that is quantitative, simple, and enables high‐throughput measurements of bacterial response to different chemicals. Using the model bacterium Escherichia coli, we demonstrated a strategy for identifying molecules that activate chemoreceptors from a diverse compound library and for determining how global behavioral strategies are tuned to chemical environments.     

Limitations to the Use of Woven Roving Glass Fibers in Plastic Composites,or the Case Against Woven Roving

Composite materials consist of at least two chemically distinct phases basically having a reinforcing material supported in a matrix material with a distinct reinforcement/matrix (R/M) interface separating the components; the components must be combined three-dimensionally. The composite has properties distinctly different from the properties of any constituents, which generally would not be achieved in any of the constituents acting alone. The principle is to use the plastic flow in the matrix to load the reinforcement in the direction of the applied load. To do this it is necessary to transfer and share the externally applied service loads of the composite through the weak matrix to the stronger reinforcement by a shear loading action. The job of the matrix is to transmit and distribute the stresses onto the individual fibers and to maintain the separation and orientation of the fibers. The interface is the critical factor that determines to what extent the potential properties of the composite will be achieved and maintained during usage. The interface must have the appropriate chemical and physical features in order to provide the necessary load transfer from the matrix to the reinforcement [1]. While the strain at the point of service loading is not uniformly distributed over the composite cross section, a finite distance away it does assume a uniform distribution. At this area the shear stress at the component interfaces is zero in the direction of the applied load [2].     

Hydrothermally Stable WO3/ZrO2–Ce0.6Zr0.4O2 Catalyst for the Selective Catalytic Reduction of NO with NH3

A new catalyst WO₃/ZrO₂–Ce_0.6Zr_0.4O₂ (15 wt % WO₃/ZrO₂:Ce_0.6Zr_0.4O₂ = 50:50) has been developed for the selective catalytic reduction of NO with NH₃. The redox component Ce_0.6Zr_0.4O₂ was dispersed on the surface of acidic WO₃/ZrO₂ by the solution combustion method showing the best NO _x reduction efficiency among the catalysts prepared by various modes of mixing of the components. The catalyst has been characterized by XRD, Raman spectroscopy and NH₃-TPD. A NO _x reduction efficiency of more than 90 % was obtained between 300 and 500 °C at α = NH_3,in/NO _x,in = 1. The catalyst showed stable NO _x reduction efficiency after hydrothermal ageing at 700 °C. Sulfur poisoning promoted the NO _x reduction efficiency at high temperatures at the expense of a reduced activity at lower temperatures, but the catalyst could be fully regenerated by heating in O₂ at 650 °C.     

Minor Role of Mitochondrial Respiration for Fatty-Acid Induced Insulin Secretion

An appropriate insulin secretion by pancreatic beta-cells is necessary to maintain glucose homeostasis. A rise in plasma glucose leads to increased metabolism and an elevated cytoplasmic ATP/ADP ratio that finally triggers insulin granule exocytosis. In addition to this triggering pathway, one or more amplifying pathways—activated by amino acids or fatty acid—enhance secretion by promoting insulin granule recruitment to, and priming at, the plasma membrane. The aim of this study was to clarify the impact of the mitochondrial respiratory activity on fatty acid-induced insulin secretion that was assessed by an extracellular flux analyzer. Treatment of isolated mouse islets with glucose (20 mM) increased insulin secretion 18-fold and correlated with ATP-synthesizing respiration. Furthermore, oxygen consumption rate (OCR) significantly increased by 62% in response to glucose, whereas the addition of palmitate resulted only in a minor increase of OCR at both 2.8 mM (11%) and 20 mM glucose (21%). The addition of palmitate showed a pronounced increase of coupling efficiency (CE) at 2.8 mM glucose but no further insulin secretion. However, treatment with palmitate at 20 mM glucose increased insulin secretion about 32-fold accompanied by a small increase in CE. Thus, fatty acid induced respiration has a minor impact on insulin secretion. Our data clearly demonstrate that fatty acids in contrast to glucose play a minor role for respiration-mediated insulin secretion. In the presence of high glucose, fatty acids contribute partially to amplifying pathways of insulin secretion by further increasing mitochondrial activity in the islets of Langerhans.     

Influence of Stress and Chemical Homogeneity on Dielectric Properties of BaTi0.9Zr0.1O3

The influence of mechanical stress and chemical homogeneity on the permittivity of BaTi_0.9Zr_0.1O₃ ceramics prepared from mixed-oxide and hydrothermal powders was studied. To reduce stress, liquid-phase sintering was applied in conjunction with a low heating rate to stimulate the formation of large grains. The influence of chemical homogeneity was studied by variations in sintering temperatures and times. For both types of ceramics, the dielectric constant at the Curie temperature was influenced by both factors, but to a different extent. In the mixed oxide ceramic, chemical homogeneity played a more prominent role, while internal stress appeared to exert a larger influence in the hydrothermal ceramics. The dielectric constant at the Curie temperature could be increased by 5%–10% by an annealing treatment at 200°C, followed by slow cooling.     

XPS analysis of wet chemical etching of GaAs(110) by Br2–H2O: comparison of emersion and model experiments

We have applied photoelectron spectroscopy to investigate the surface composition after different surface treatments involving Br₂–H₂O mixtures in order to study wet chemical etching. Emersion experiments from Br₂–H₂O solution are compared with model experiments, in which Br₂–H₂O adsorbate and coadsorbate mixtures react with clean GaAs(110) surfaces. Our results indicate that Ga- and As-bromides formed initially are hydrolyzed to form the respective oxides. Without addition of Br₂, only slight oxidation of the surface takes place. There is an enrichment of Ga due to loss of As both in adsorption as well as in emersion experiments. Since in emersion experiments only a final situation is analyzed, the relative influence of surface reactivity and subsequent solvation effects cannot be distinguished easily, while model experiments give clear information on reaction products formed intermediately. However, model experiments differ in environment and temperature from the real solid–liquid interface. The presented results demonstrate that a combination of emersion and model experiments provide valuable insight into the mechanism of wet chemical etching on a microscopic level.     

Deep HDS over NiMo/Zr-SBA-15 catalysts with varying MoO3 loading

In the present work, with the aim of searching for new, highly effective catalysts for deep HDS, a series of NiMo catalysts with different MoO₃ loadings (6–30 wt.%) was prepared using SBA-15 material covered with ZrO₂-monolayer as a support. Prepared catalysts were characterized by N₂ physisorption, small- and wide-angle XRD, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, SEM-EDX and HRTEM, and their catalytic activity was evaluated in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). It was observed that ZrO₂ incorporation on the SBA-15 surface improves the dispersion of the Ni-promoted oxidic and sulfided Mo species, which were found to be highly dispersed, up to 18 wt.% of MoO₃ loading. Further increase in metal charge resulted in the formation of MoO₃ crystalline phase and an increase in the stacking degree of the MoS₂ particles. All NiMo catalysts supported on ZrO₂-modified SBA-15 material showed high activity in HDS of 4,6-DMDBT. The best catalyst having 18 wt.% MoO₃ and 4.5 wt.% NiO was almost twice more active than the reference NiMo/γ-Al₂O₃ catalyst. High activity of NiMo/Zr-SBA-15 catalysts and its evolution with metal loading was related to the morphological characteristics of the MoS₂ active phase determined by HRTEM.