Search results for "Stability."
showing 10 items of 3015 documents
Hydroxamate Titanium–Organic Frameworks and the Effect of Siderophore-Type Linkers over Their Photocatalytic Activity
2019
The chemistry of metal–organic frameworks (MOFs) relies on the controlled linking of organic molecules and inorganic secondary building units to assemble an unlimited number of reticular frameworks. However, the design of porous solids with chemical stability still remains limited to carboxylate or azolate groups. There is a timely opportunity to develop new synthetic platforms that make use of unexplored metal binding groups to produce metal–linker joints with hydrolytic stability. Living organisms use siderophores (iron carriers in Greek) to effectively assimilate iron in soluble form. These compounds make use of hard oxo donors as hydroxamate or catecholate groups to coordinate metal Lew…
Numerical approach for signal delay in general distributed networks
2003
The authors consider a general network with telegraph equations modelling distributed elements and having, additionally, nonlinear capacitors. A global asymptotic exponential stability of the solution is given. A simple computable upper bound of the delay time is given. Numerical examples illustrate the usefulness of the results. >
A Novel Approach to Introducing Adaptive Filters Based on the LMS Algorithm and Its Variants
2004
This paper presents a new approach to introducing adaptive filters based on the least-mean-square (LMS) algorithm and its variants in an undergraduate course on digital signal processing. Unlike other filters currently taught to undergraduate students, these filters are nonlinear and time variant. This proposal introduces adaptive filtering in the context of a linear time-invariant system using a real problem. In this way, introducing adaptive filters using concepts already familiar to the students motivates their interest through practical application. The key point for this simplification is that the input to the filter is constant so that the adaptive filter becomes linear. Therefore, a …
Novel silicon microparticles to improve sunlight stability of raw polypropylene
2015
Oxidation of polyolefins by ultraviolet/visible irradiation is a significant limitation for their use in several technological applications. The use of high-tech additives such as silicon microparticles becomes a compositing strategy that can improve the performance of these materials at long-term service conditions. Silicon particles were added to non-additivated raw polypropylene (PP) prepared by hot melt extrusion and subjected to accelerated sunlight irradiation tests. The stability of thermal properties, mechanical performance and thermal decomposition behaviour of composites was evaluated by differential scanning calorimetry, dynamic mechanical thermal analysis and thermogravimetry. T…
New Molecular-Based Materials for Enabling Electro-Optical Bistability in the Silicon Photonics Platform
2019
Electro-optical bistability is a functionality which can be crucial for a wide range of applications as it can enable non-volatile and ultra-low power switching performance. We investigate the integration of a molecular-based material presenting a Spin Crossover (SCO) effect in the silicon platform for enabling optical bistability. The SCO phenomenon involves a switching process between two molecular spin states. This spin transition comes along with a change in the optical refractive index that can be switched by different external stimuli such as a variation of temperature or light irradiation and which has a hysteretic behaviour. The SCO material can be synthetized as nanoparticles so th…
Control of the pore wall thickness and thermal stability in low-cost bimodal porous silicas
2019
Abstract A new hierarchical bimodal mesoporous silica, labelled as UVM-12 (acronym of University of Valencia Materials), has been prepared by using a solution of sodium silicate as low-cost silicon source. The final self-assembling between cationic micelles of CTAB and anionic inorganic Si-based oligomers occurs in a homogeneous aqueous medium. The reaction is carried out from low-sized building blocks through a bottom-up approach. The UVM-12 solids combine two mesopore systems according to N2 adsorption–desorption isotherms, what is corroborated by TEM micrographs and XRD patterns. This material has been inorganically modified by incorporation of Al or Ti (M-UVM-12, M = Al, Ti) without alt…
Numerical investigation of the influence of EM-fields on fluid motion and resistivity distribution during floating-zone growth of large silicon singl…
2001
The floating-zone-process with needle-eye inductor is a complex process with many coupled parameters that have nonlinear influence on the process stability and resistivity distribution in the silicon single crystal. To fulfill the requirements of semiconductor industry for tighter specification of resistivity distribution, additional means like magnetic fields can be used to reach a more homogeneous resistivity distribution without disturbing process stability. The current paper analyses the influence of static and alternating fields on the fluid motion and macroscopic and microscopic resistivity profile by means of numerical calculations. It is found that with a lower frequency of the HF-i…
Multiarm cyclam-grafted mesoporous silica: a strategy to improve the chemical stability of silica materials functionalized with amine ligands
2009
We have explored in this work the stability and the reactivity of multiarm cyclam-grafted mesoporous silica samples in aqueous solution. A series of hybrid materials have been prepared by grafting silylated cyclam molecules bearing one, two, or four silyl groups onto both amorphous silica gel (K60) and ordered mesoporous silica (SBA15). Under these conditions, cyclam moieties are attached to the silica walls via one, two, or four arms. Various physicochemical techniques have been applied to characterize the functionalized solids (elemental analysis, 1H-29Si and 1H-13C CPMAS NMR, and N2 adsorption-desorption isotherms). The interest in two and four arms for improving the chemical stability i…
Generalized singly-implicit Runge-Kutta methods with arbitrary knots
1985
The aim of this paper is to derive Butcher's generalization of singly-implicit methods without restrictions on the knots. Our analysis yields explicit computable expressions for the similarity transformations involved which allow the efficient implementation of the first phase of the method, i.e. the solution of the nonlinear equations. Furthermore, simple formulas for the second phase of the method, i.e. computation of the approximations at the next nodal point, are established. Finally, the matrix which governs the stability of the method is studied.
A proof of bistability for the dual futile cycle
2014
Abstract The multiple futile cycle is an important building block in networks of chemical reactions arising in molecular biology. A typical process which it describes is the addition of n phosphate groups to a protein. It can be modelled by a system of ordinary differential equations depending on parameters. The special case n = 2 is called the dual futile cycle. The main result of this paper is a proof that there are parameter values for which the system of ODE describing the dual futile cycle has two distinct stable stationary solutions. The proof is based on bifurcation theory and geometric singular perturbation theory. An important entity built of three coupled multiple futile cycles is…