Copper and niobium are mutually immiscible in the solid state and exhibit a large positive enthalpy of mixing in the liquid state. Using vapour quenching via magnetron co-sputter deposition, far-from equilibrium amorphous Cu–Nb films have been deposited which exhibit a nanoscale phase separation. Annealing these amorphous films at low temperatures (~200?°C) initiates crystallization via the nucleation and growth of primary nanocrystals of a face-centred cubic Cu-rich phase separated by the amorphous matrix. Interestingly, subsequent annealing at a higher temperature (>300?°C) leads to the polymorphic nucleation and growth of large spherulitic grains of a body-centred cubic Nb-rich phase within the retained amorphous matrix of the partially crystallized film. This sequential two-stage crystallization process has been investigated in detail by combining transmission electron microscopy [TEM] (including high-resolution TEM) and atom probe tomography studies. These results provide new insights into the crystallization behaviour of such unusual far-from equilibrium phase-separated metallic glasses in immiscible systems. 相似文献
The use of crosslinked polystyrene anion-exchange resin as a support for borohydride ions made it possible to reduce conjugated olefinic bonds selectively under very mild conditions. The isolation of the reduced products by a simple filtration and evaporation process is another interesting feature of this reaction. 相似文献
The mobility of a two-dimensional electron gas (2DEG) in a rectangular potential well formed in a AlGaAs/GaAs/AlGaAs structure scattered by polar-optic phonon is calculated by an iterative solution of Boltzmann equation. The values are significantly different from those calculated by using a relaxation time. The polar-optic mobility is found to dominate over acoustic mobility over a temperature range of 100–300 K when the well thickness is about 10 nm. The mobility values for 2DEG are, however, found to be lower than the bulk values. 相似文献
A whole range of Robson-type tetraiminodiphenol macrocyclic ligands have been prepared as their perchlorate salts [H4L](ClO4)2 in high yield (ca. 90%) by a single-step [2 + 2] condensation reaction between 4-methyl(or tert-butyl)-2,6-diformyl(or diacyl)phenols and alpha,omega-diaminoalkanes (C2-C12) in the presence of acetic acid and NaClO4. The reduction of these 18- to 38-membered macrocyclic salts with NaBH4 have afforded corresponding tetraaminodiphenol macrocycles H2L'. The X-ray crystal structures of two of the tetraiminodiphenol macrocycles with the C2 and C4 lateral chains have been determined, and the optimized configurations for all of the macrocycles have been obtained by molecular mechanics calculations. The macrocycles have been characterized by elemental analysis and by IR, absorption, emission, and NMR spectroscopic study. The protonated tetraiminodiphenol macrocycles exhibit strong fluoroscence in methanol, acetonitrile, and nitromethane and undergo quenching when treated with triethylamine. The neutral macrocycles H2L, isolated by treating [H4L](ClO4)2 with excess of triethylamine, lack luminescence, as do the reduced tetraaminodiphenol macrocycles H2L'. The hydrolytic cleavage of [H4L](ClO4)2 has been studied. 相似文献
A simple model system has been used to develop thermodynamics and kinetics for bulk and surface aggregation processes capable of competing with each other. The processes are the stepwise aggregation of monomers in a fluid medium and on an impenetrable solid surface bounding the fluid medium, besides the adsorption and desorption of the same species at the solid-fluid interface. Emphasis is on aggregation processes in the high friction limit. The theoretical model is used to compare the kinetics and thermodynamics of the processes and to infer the conditions in which one process dominates another, in the high friction limit, such as in a liquid. The motivation of this study is obtaining insight into competition between aggregation in solution and on an adjoining surface, such as a cell membrane. 相似文献
Langmuir film behavior of bovine lipid extract surfactant (BLES), mixed with cholesterol (CHOL) and cholesterol palmitate (CHOLP), has been studied by surface pressure (pi)-area (A) measurements. Associative interactions, observed for both systems, were less favored at lower BLES content. The presence of unsaturated phospholipids and surfactant proteins in BLES favored the association. Miscibility of BLES was better with CHOLP than with CHOL at all compositions, indicating more compact packing of the BLES-CHOLP than of the BLES-CHOL system. The most stable mixtures were found at 30-40 mol% CHOL and at low pi and at 20-25 mol% CHOLP but at higher pi. These results suggest that BLES-CHOL miscibility is better at low pi and low CHOL concentrations, while BLES-CHOLP miscibility is better at high pi and high CHOLP concentrations. 相似文献
To explore the impact of pest-control strategy on integrated pest management, a three-dimensional (3D) fractional- order slow–fast prey–predator model is introduced in this article. The prey community (assumed as pest) represents fast dynamics and two predators exhibit slow dynamical variables in the three-species interacting prey–predator model. In addition, common enemies of that pest are assumed as predators of two different species. Pest community causes serious damage to the economy. Fractional-order systems can better describe the real scenarios than classical-order dynamical systems, as they show previous history-dependent properties. We establish the ability of a fractional-order model with Caputo’s fractional derivative to capture the dynamics of this prey–predator system and analyze its qualitative properties. To investigate the importance of fractional-order dynamics on the behavior of the pest, we perform the local stability analysis of possible equilibrium points, using certain assumptions for different sets of parameters and reveal that the fractional-order exponent has an impact on the stability and the existence of Hopf bifurcations in the prey–predator model. Next, we discuss the existence, uniqueness and boundedness of the fractional-order system. We also observe diverse oscillatory behavior of different amplitude modulations including mixed mode oscillations (MMOs) for the fractional-order prey–predator model. Higher amplitude pest periods are interspersed with the outbreaks of small pest concentration. With the decrease of fractional-order exponent, small pest concentration increases with decaying long pest periods. We further notice that the reduced-order model is biologically significant and sensitive to the fractional-order exponent. Additionally, the dynamics captures adaptation that occurs over multiple timescales and we find consistent differences in the characteristics of the model for various fractional exponents.
The decision to invest in new ventures is characterized by incomplete information, where some measures of firm performance are quantitative, while some others are substituted by qualitative indicators. Qualitative attributes are defined in a relative sense. We develop a decision support model for identifying successful new ventures. The model integrates quantitative and qualitative variables through the use of the Analytic Hierarchy Process (AHP). The decision model gains in predictive accuracy through the use of qualitative attributes, and AHP imparts robustness to the qualitative measures. 相似文献
Highlights? Raman spectroscopy requires no dye probe but still enables molecular imaging ? Stable-isotope labeling distinguishes between existing and newly formed proteins ? Protein localization to lipid droplets has been revealed in fission yeast ? The colocalization phenomenon is associated with starvation 相似文献