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1.
The kinetics of noble metal nanoparticle formation in bottom-up syntheses are important for controlling and optimizing these methods. Hence, experimental probes that are easily accessible to most laboratories are also of interest. We collected kinetic curves for the formation of silver nanoparticles in a modified Turkevich method with citrate acting as the reducing and stabilizing agent by (i) measuring the change in silver nanoparticle surface plasmon resonance by UV-visible spectroscopy, a somewhat indirect method, and then also by (ii) measuring the change in silver ion concentration by ion-selective electrode potentiometry and/or atomic absorption spectroscopy, two more direct methods. The resulting sigmoidal kinetic curves were curvefitted with the Finke-Watzky two-step kinetic model of slow, continuous nucleation and fast autocatalytic growth to extract average rate constants. We found that the kinetic curves obtained by following the change in silver ion concentration were apparent mirror images of those constructed by following the change in nanoparticle surface plasmon resonance, and that their respective curvefits displayed the same sigmoidal characteristics. The resultant values of the rate constants for nucleation and growth overlapped within experimental error between the methods and showed similar trends over the range of citrate concentrations studied. The use of multiple probes in this work to follow the kinetics of nanoparticle formation helps fill a need for the comparison and evaluation of different methods available to scientists, particularly those considered easily accessible. 相似文献
2.
Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing. In this work, we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin-orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier. Therefore, the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field. Moreover, we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior. This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing. 相似文献
3.
Application of the Šesták-Berggren Equation to Organic and Inorganic Materials of Practical Interest
A. K. Burnham 《Journal of Thermal Analysis and Calorimetry》2000,60(3):895-908
Reactions that have an initial acceleratory period are common in both organic and inorganic systems. The Šesták-Berggren equation,
dx/dt= -kx
n(1-x)m[-ln(x)]p, with p set to zero (also called the extended Prout-Tompkins (PT) equation) is an excellent empirical kinetic law for many of these
systems. In this work, it is shown to fit both isothermal and constant heating rate pyrolysis data for a well-preserved algal
kerogen in a petroleum source rock and two synthetic polymers (polycarbonate and poly-ether-etherketone), dehydration of calcium
oxalate monohydrate, decomposition of ammonium percholorate, and diffusive release of gas implanted in materials. Activation
energies derived by non-linear regression to multiple experiments are consistent with those derived by simple isoconversional
methods. Errors caused by misapplication of first-order kinetics to single-heating-rate data are discussed briefly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Burkhard Lenze 《Numerical Functional Analysis & Optimization》2013,34(7-8):909-913
We prove a uniform density result for three-layer feedforward sigma-pi neural networks of hyperbolic type. 相似文献
5.
Dan Sheng Yu 《数学学报(英文版)》2013,29(10):2013-2026
In this paper, we introduce a type of approximation operators of neural networks with sigmodal functions on compact intervals, and obtain the pointwise and uniform estimates of the ap- proximation. To improve the approximation rate, we further introduce a type of combinations of neurM networks. Moreover, we show that the derivatives of functions can also be simultaneously approximated by the derivatives of the combinations. We also apply our method to construct approximation operators of neural networks with sigmodal functions on infinite intervals. 相似文献
6.
In this paper,the technique of approximate partition of unity is used to construct a class of neural networks operators with sigmoidal functions.Using the modulus of continuity of function as a metric,... 相似文献
7.
S‐shaped curves arise in many calibration assays. They are typically modeled using an empirically chosen nonlinear function. Nonparametric alternatives usually perform poorly because there are often insufficient data points and there are difficulties in enforcing the required asymptotic behavior. We propose an alternative approach using a b‐spline basis adapted to produce lower and upper asymptotes in the fitted curves. Its main advantage is that, with pre‐determined knot positions, the model is linear in the parameters and so is more numerically stable than a nonlinear model; this has advantages in, for example, fitting a mixed model to multiple curves. We explore the performance of this approach using data from a single radioimmunoassay for cortisol and from a set of 96 ELISA assays for the herbicide atrazine. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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9.
Using some regular matrices we present a method to express any multivariate algebraic polynomial of total order n in a normal form. Consequently, we prove constructively that, to approximate continuous target functions defined on some compact set of ? d , neural networks are at least as good as algebraic polynomials. 相似文献
10.
B. J. Love F. Piguet Ruinet F. Teyssandier 《Journal of Polymer Science.Polymer Physics》2008,46(21):2319-2325
Experiments were conducted to evaluate the influence of ambient photoconversion on rheology for a range of photopolymerizable urethane dimethacrylate (UDMA) resins containing varying amounts of three comonomers including 1,6 hexane diol‐dimethacrylate (HDDMA), an alkoxylated cyclohexane dimethanol diacrylate monomer (CD‐582), and hydroxyethyl methacrylate (HEMA). Experiments were performed both as a function of composition and time‐dependent dose varying the intensity using a photorheometer. A semilog‐based sigmoidal model allowed the determination of four physical model parameters to define the relationship between reaction kinetics and its dynamic influence on viscosity. We have observed induction times and viscosity changes associated with the model that shows a trend in reaction kinetics in the following order from most to least reactive: UDMA > CD582 > HDDMA > HEMA. With increasing amounts of reactive diluent included in the formulation, the kinetics of reaction was more sluggish. The value of this sigmoidal model is that it could help define formulation and process conditions most likely to control crosslinking to maximize dimensional stability or other thermophysical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2319–2325, 2008 相似文献