Nafion SAC-13 effectively activates hexamethyldisilazane (HMDS) for the efficient and selective silylation of alcohols. Primary, secondary, and tertiary alcohols and phenols are efficiently converted to their corresponding silylethers in short reaction times (4-8 min) with excellent yield at rt under solvent-free condition. Simple and clean reactions, high yield of the products and efficient recycling of the catalyst are the salient features of this methodology. 相似文献
Applied Biochemistry and Biotechnology - In this study, a homogenization-based extraction method was developed and was compared to five conventional methods of squalene extraction. Squalene... 相似文献
The structure consists of two acetyl-substituted PCU cages linked by a diyne fragment. The conformation about the linker is midway between staggered and eclipsed, and the acetyl groups are somewhat distorted due to the proximity to the bulky cage units. 相似文献
In this paper we consider a generalization of Brinkman's equation governing the flow of an incompressible fluid through a porous medium to take into account the variation of the viscosity with the pressure. There is overwhelming evidence that the viscosity depends on pressure and that this dependence is exponential. We also consider the problem of a barotropic fluid in which both the viscosity and the density depend upon the pressure. We use a homogenization procedure, that exploits a multiple scale structure possessed by a solid porous medium, a `micro‐scale' comparable to the pore size and a `macro‐scale' associated with the global size of the body, to carry out a multiple‐scale asymptotic analysis. The ratio of the micro‐scale length to the macro‐scale length provides a small parameter that is a natural parameter with which to carry out a perturbation analysis. The perturbation procedure leads to a systematic methodology by means of which we can obtain equations at different orders of the small parameter. Specifically, we study some simple boundary value problems corresponding to one‐dimensional flows. We find that while the dependence of the viscosity on the pressure can have a significant effect on the nature of the solution, so much so that the solution is completely different in comparison to the constant viscosity case Brinkman's equation, we find that the dependence of the density on the pressure has little or no effect on the nature of the solution. 相似文献
Analyzing the chaos and bursting phenomenon of neurons has been of interest in the past decade. In this paper, we discuss an extended Hindmarsh-Rose neuron model by taking into consideration the slowly interacting cell phenomenon due to the calcium ions. In the extended model, we consider the effect of an external forcing current, and the electromagnetic coupling between the magnetic flux and the membrane potential of the neuron. We analyze the modified neuron model in the presence of periodic and quasi-periodic excitations. A more complex chaotic behavior (hyperchaos) is identified in the neuron model. The results also demonstrate the multistable nature, which was not explored earlier. To discuss the dynamical behavior of the modified neuron in a network, we construct a ring network of neurons and capture the spatiotemporal patterns of the neuron in the network, in the presence of different excitations.
This letter gives a general review on the monostability, bistability, periodicity and chaos in gene regulatory network. Some simple motifs that generate monostability, bistability, periodicity and chaos are analytically and numerically reported. Further research directions of the nonlinear dynamics of gene regulatory network are discussed. 相似文献
We report a custom-geometry linear ion trap designed for fluorescence spectroscopy of gas-phase ions at ambient to cryogenic temperatures. Laser-induced fluorescence from trapped ions is collected from between the trapping rods, orthogonal to the excitation laser that runs along the axis of the linear ion trap. To increase optical access to the ion cloud, the diameter of the round trapping rods is 80% of the inscribed diameter, rather than the roughly 110% used to approximate purely quadrupolar electric fields. To encompass as much of the ion cloud as possible, the first collection optic has a 25.4 mm diameter and a numerical aperture of 0.6. The choice of geometry and collection optics yields 107 detected photons/s from trapped rhodamine 6G ions. The trap is coupled to a closed-cycle helium refrigerator, which in combination with two 50 Ohm heaters enables temperature control to below 25 K on the rod electrodes. The purpose of the instrument is to broaden the applicability of fluorescence spectroscopy of gas-phase ions to cases where photon emission is a minority relaxation pathway. Such studies are important to understand how the microenvironment of a chromophore influences excited state charge transfer processes.
