The effect of structural properties of natural silica precursors in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100 °C

The low-temperature synthesis of zeolite ZSM-5 below 100 °C is gaining new attention. This is due to the fact that such synthesis may simultaneously implement the introduction of mesopores into crystalline microporous zeolite structure. Herein, we report the use of natural silica precursors from rice husks in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100 °C and their structural properties which govern the course of crystallization. Rice husks are agricultural wastes with high silica content, which should be exploited to give a positive impact, i.e. highly value-added materials. In this study, the amorphous silica from rice husks was extracted using sequential base-acid treatment. The extracted silica was similarly reactive as Ludox HS-40, even with the reduced amounts of the organic structure-directing agent (OSDA). The product was highly crystalline ZSM-5 with spherical morphology composed of small crystallites, enabling the presence of intercrystallite mesopores. The subjection of extracted silica into the calcination at 550 °C for 6 h, prior to the low-temperature synthesis, altered the silica structure via hydroxyl condensation. The distinct structural properties affected the occurring crystallization in which the resulted products were ZSM-5–disordered-mesoporous silica composites. The possible mechanisms of these two different results may involve the dual roles of tetrapropylammonium ion (TPA⁺) as zeolite OSDA and non-templating structure directing agent. These insights were based on the spectroscopic (FTIR, Raman, ²⁹Si and ²⁷Al MAS NMR spectroscopy), microscopic (TEM and HRTEM) and physicochemical characterizations (XRD and N₂ adsorption-desorption isotherm).     

Improving time integration scheme for FEM analysis of MTL problems

This paper presents improved algorithm for electromagnetic transient calculations on multiconductor transmission line (MTL) achieved by improvement of the time integration when forming a local system of equations for a finite element. Improvement of accuracy was obtained by using Heun's method. Previously developed local system of equations of MTL has been obtained using the generalized trapezoidal rule (ϑ -method). The use of the generalized trapezoidal rule for the time integration sometimes causes numerical oscillations or numerical diffusion of numerical solutions. Numerical solutions obtained using Heun's method and using the generalized trapezoidal rule for different values of a time integration parameter are compared with analytical solution. It has been shown that Heun's method yields the results with much higher accuracy comparing to results obtained by generalized trapezoidal rule.     

Grounding autonomy adjustment on delegation and trust theory

In this paper we will briefly present the adjustment of autonomy as the problem of adjusting the level and the kind of delegation. The cncept of autonomy here considered is about a delegated task (or role). It is argued that by a careful analysis of the various aspects of delegation (openness, strength, etc.) it is possible to represent and model many dimensions of autonomy and consequently both the reasons and the ways to introduce a dynamic level of control.     

Model for Predicting Floods due to Earthen Dam Breaching. II: Comparison with Other Methods and Predictive Use

A sensitivity analysis of the model presented in the companion paper is made and, on the basis of the results a criterion is proposed for the choice of values to assign to the side slopes of the breach, in order to use the model for prediction. Moreover, the sensitivity analysis shows that the outflow hydrograph and its peak value depend not only on the dam height and the stored volume, but also on the vertical distribution of the water mass in the reservoir. The model is compared with some previously published methods and the disadvantages, limitations, and errors that can be made using parametric models and predictive equations are pointed out. Finally, easy to use equations interpolating the numerical results of the model are provided that predict not only the peak discharge but the whole outflow hydrograph for overtopping failures.     

Platinum(II) Diphosphinamine Complexes for the Efficient Hydration of Alkynes in Micellar Media

Highly active monomeric bis‐cationic platinum(II) catalysts bearing small bite angle diphosphinamine [N,N‐bis(diarylphosphino)amine] ‘PNP’ ligands efficiently catalyze Markovnikov hydration of terminal and internal alkynes to the corresponding ketones in water. Catalyst solubilization in water is achieved via ion pairing with anionic micelles formed by surfactant addition. The micelles ensure dissolution of apolar alkynes and promote the intimate contact between reagents and catalyst, while in organic‐water media in the absence of surfactants the reaction is sluggish. Hydration products can be isolated by means of extraction with an apolar solvent and the catalyst, that remains confined in the aqueous phase, can be recycled up to four times without loss of catalytic activity.     

A comparison of forward-boundary-integral andparabolic-wave-equation propagation models

The parabolic-wave equation and its variants have provided the theoretical framework for most practical forward-propagation models. Split-step integration generates an easily obtained, robust solution for most applications. Irregular boundaries can be incorporated by using a conformal mapping technique introduced by Beilis and Tappert (1979) and refined by Donohue and Kuttler (see ibid., vol.48, p.260-77, 2000). In an earlier paper, we demonstrated an alternative method that incorporates a numerical solution to the forward-boundary-integral equation within each split-step cycle. This paper compares predictions of forward propagation obtained by these two distinctly different methods. The results confirm that the PWE-based method is very accurate for smoothly varying surfaces and that it captures the primary forward structure even in the presence of unresolved surface detail. The moderate loss of fidelity is often an acceptable trade for increased computational efficiency. There are situations, however, where the details of the surface structure are important. Furthermore, the induced surface currents are unique to the forward-boundary-integral method. We illustrate their use by calculating the bistatic scatter that would he measured from an isolated surface segment. We show that the scattered field measured in this way can be normalized to form a bistatic scatter function only when the illuminating beam is tilted slightly toward the surface. We interpret this disparity as a breakdown in concept that underlies a local scattering function     

Structural characterization of deformed crystals by analysis of common atomic neighborhood

Simulations of crystal deformation and structural transformation may generate complex datasets involving networks with million to billion chemical bonds which makes local structure analysis a challenge. An ideal analysis method must recognize perfect crystal structures, such as face-centered cubic, body-centered cubic and hexagonal close packed, and differentiate structural defects such as dislocations, stacking faults, grain boundaries, cracks and surfaces. Currently a few methods are used for this purpose, e.g., the Common Neighbor Analysis (CNA) and the Centrosymmetry Parameter (CSP). This paper proposes an alternative method based on the calculation of a single parameter that depends on the common atomic neighborhood. We validate the method characterizing local structures in complex molecular-dynamics datasets, clarifying its advantages over the CNA and the CSP methods.     

“Smart” TDDB algorithm for investigating degradation in high-κ gate dielectric stacks under constant voltage stress

A new “smart” algorithm with adaptive testing is developed for automatically monitoring gate dielectric degradation during CVS using SILC. In this approach, stress current is monitored with a sampling rate as fast as ∼2 ms/point while SILC data are collected based on stress current changes and/or time intervals. This automated test was applied to study degradation of nMOS transistors with TiN/HfO₂ gate stacks where changes in the SILC data correlate directly with transitions in the stress current. From this SILC data, the differential resistance can be extracted and used to monitor conductivity throughout the degradation phase until breakdown.     

Decoupling of cold-carrier effects in hot-carrier reliability assessment of HfO/sub 2/ gated nMOSFETs

To understand the intrinsic effect of a hot-carrier injection on high-/spl kappa/ dielectrics free from concurrent cold-carrier trapping, the authors have investigated a hot-carrier-induced damage with channel hot-carrier stresses and substrate hot-carrier stress. Compared to substrate hot-carrier stress, the channel hot-carrier stress shows a more significant cold-carrier-injection effect. By using a detrapping bias, they were able to decouple the effect of cold-carrier trapping from the permanent trap generation induced by the hot-carrier injection. As channel hot-carrier stress bias was reduced, a portion of cold-carrier trapping increased and a portion of interface trap generation decreased.