Stability of Pt near surface alloys under electrochemical conditions: a model study

2014 ◽  
Vol 16 (31) ◽  
pp. 16615-16622 ◽  
Author(s):  
Xiaoming Zhang ◽  
Shansheng Yu ◽  
Weitao Zheng ◽  
Ping Liu
Keyword(s):  
Fuel Cell ◽  
Automotive Applications ◽  
Surface Alloys ◽  
Near Surface ◽  
Model Study ◽  
The Stability

The stability is one of the key requirements for commercializing the fuel cell electrocatalysts in automotive applications.

scholarly journals Stability of SG1 nitroxide towards unprotected sugar and lithium salts: a preamble to cellulose modification by nitroxide-mediated graft polymerization

2013 ◽  
Vol 9 ◽  
pp. 1589-1600 ◽  
Author(s):  
Guillaume Moreira ◽  
Laurence Charles ◽  
Mohamed Major ◽  
Florence Vacandio ◽  
Yohann Guillaneuf ◽  
...  
Keyword(s):  
Graft Polymerization ◽  
Polymer Chains ◽  
Lithium Salts ◽  
Organic Media ◽  
Cellulose Derivatives ◽  
Cellulose Modification ◽  
Model Study ◽  
The Stability ◽  
Grafting From ◽  
Intramolecular Hydrogen

The range of applications of cellulose, a glucose-based polysaccharide, is limited by its inherently poor mechanical properties. The grafting of synthetic polymer chains by, for example, a “grafting from” process may provide the means to broaden the range of applications. The nitroxide-mediated polymerization (NMP) method is a technique of choice to control the length, the composition and the architecture of the grafted copolymers. Nevertheless, cellulose is difficult to solubilize in organic media because of inter- and intramolecular hydrogen bonds. One possibility to circumvent this limitation is to solubilize cellulose in N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA) with 5 to 10 wt % of lithium salts (LiCl or LiBr), and carry out grafted polymerization in this medium. The stability of nitroxides such as SG1 has not been studied under these conditions yet, even though these parameters are of crucial importance to perform the graft modification of polysaccharide by NMP. The aim of this work is to offer a model study of the stability of the SG1 nitroxide in organic media in the presence of unprotected glucose or cellobiose (used as a model of cellulose) and in the presence of lithium salts (LiBr or LiCl) in DMF or DMA. Contrary to TEMPO, SG1 proved to be stable in the presence of unprotected sugar, even with an excess of 100 molar equivalents of glucose. On the other hand, lithium salts in DMF or DMA clearly degrade SG1 nitroxide as proven by electron-spin resonance measurements. The instability of SG1 in these lithium-containing solvents may be explained by the acidification of the medium by the hydrolysis of DMA in the presence of LiCl. This, in turn, enables the disproportionation of the SG1 nitroxide into an unstable hydroxylamine and an oxoammonium ion. Once the conditions to perform an SG1-based nitroxide-mediated graft polymerization from cellobiose have been established, the next stage of this work will be the modification of cellulose and cellulose derivatives by NMP.

A Model Study of Instabilities Present in the Mean-Field Description and in Linearized Correlation Schemes

1989 ◽  
Vol 44 (2) ◽  
pp. 117-124
Author(s):  
Michael C. Böhm ◽  
Gerd Bubeck ◽  
Andrzej M. Oles
Keyword(s):  
Theoretical Calculations ◽  
Mean Field ◽  
Numerical Data ◽  
Local Approach ◽  
Stability Range ◽  
Hartree Fock ◽  
Model Study ◽  
Correlation Models ◽  
The Stability ◽  
Hf Wave

Abstract In this work we discuss the cooperative occurrence of instabilities in the Hartree-Fock (HF) approximation and linearized correlation models. Both breakdown phenomena can be analyzed via eigenvalues of characteristic matrices. The well known HF instabilities follow from a quasidegeneracy between the symmetry-adapted mean-field state and singly excited configurations. Quasi-degeneracies between the HF wave function and doubly excited configurations restrict the applicability of linearized correlation models. In the theoretical calculations the method of the local approach (LA) has been employed to derive the correlated ground state. For a system of the general topology XH2 (X = C, Si, etc.) the bond orbital approximation (BOA) has been used to derive analytic formulae indicating the stability range of linearized correlation schemes. Numerical calculations on the basis of a simple model-Hamiltonian are given for the π systems C2H4 and C2H2, respectively, which have been studied as a function of the CC bondlength. The comparison of the respective numerical data indicates that both breakdown phenomena are enhanced via coupling terms between strongly correlated bonds.

Underground Barrier Protection against the Spread of Vibration - A Model Study

2014 ◽  
Vol 1020 ◽  
pp. 451-456
Author(s):  
Tomáš Petřík ◽  
Eva Hrubesova ◽  
Miroslav Pinka ◽  
Alice Hastíková
Keyword(s):  
Finite Element Method ◽  
Urban Areas ◽  
Seismic Waves ◽  
Static Load ◽  
Geological Environment ◽  
The Finite Element Method ◽  
Ground Vibrations ◽  
Industrial Activity ◽  
Model Study ◽  
The Stability

The designs of the buildings are in addition to the static load exposed to ground vibrations spreading from the surrounding geological environment. Ground vibrations, which are produced by anthropogenic phenomena, are not usually the crucial load for the stability of the building. But this load have an adversely affect the walls of buildings or sensitive equipment in these buildings. This article will be deal with model study of underground barriers utilized as a protection against the spread of ground vibrations in geological environment. These underground barriers maybe used in the vicinity of roads or railway lines or in urban areas around the halls with heavy industrial activity. Material of underground barriers will be designed from material with different parameters, so that it could be assessed the best variant in terms of absorption of seismic waves. The different variations of the thickness of underground barriers and different distances from the source of vibration will be designed in the analysis. The analysis will be performed in mathematical models that will be created in the software’s based on the finite element method.

Enterprises' Participation in Energy-Saving Activities' Motivation Mechanism Model Study

2013 ◽  
Vol 869-870 ◽  
pp. 404-407
Author(s):  
Rong Sheng Lv ◽  
Hui Ran Liu
Keyword(s):  
Energy Saving ◽  
Linear Time ◽  
Influential Factors ◽  
Research Review ◽  
Motivation Mechanism ◽  
Linear Time Invariant ◽  
Mechanism Model ◽  
Model Study ◽  
The Stability ◽  
Linear Time Invariant System

Based on the research review about enterprises' participation in energy-saving activities' influential factors, we defined the motivation mechanism of enterprises' participation in energy-saving activities. Decision Preference, goal, pressure, energy efficiency, dissemination and diffusion, government supports and other influential factors were analyzed. In this paper, through the establishment of assumptions, a variable interacted motivation mechanism linear time-invariant system was built and the stability of the system was analyzed. Finally, we proposed the motivations of enterprises' participation in energy-saving activities and the interactions among influencing factors.

SIMULTANEOUS EFFECT OF TWO TOXICANTS ON BIOLOGICAL SPECIES: A MATHEMATICAL MODEL

1996 ◽  
Vol 04 (01) ◽  
pp. 109-130 ◽  
Author(s):  
J.B. SHUKLA ◽  
B. DUBEY
Keyword(s):  
Mathematical Model ◽  
Emission Rate ◽  
Biological Species ◽  
The Other ◽  
Washout Rate ◽  
Extinction Rate ◽  
Growth And Survival ◽  
Simultaneous Effect ◽  
Model Study ◽  
The Stability

In this paper, a mathematical model to study the simultaneous effect of two toxicants (one is more toxic than the other) on the growth and survival of a biological species is proposed. The cases of instantaneous spill, constant and periodic emissions of each of the toxicant into the environment are considered. It is shown that in the case of an instantaneous spill of each of the toxicant into the environment, the species after its initial decrease in density may recover to its original level after a period of time, the magnitude of which depends on the toxicity and washout rate of each of the toxicant. However, if both the toxicants are emitted with constant rates, the species in the habitat is doomed to extinction sooner than the case of a single toxicant having the same influx and washout rates as one of them, the extinction rate becoming faster with the increase in toxicity and emission rate of the other toxicant. It is also shown that for a small amplitude periodic emission of the toxicant with a constant mean, the stability behavior of the system is same as that of the case of the constant emission. It is found further through the model study that if suitable efforts are made to reduce the emission rate of each of the toxicant at the source and its concentration in the environment by some removal mechanism, an appropriate level of species density can be maintained.

Etude en modèle réduit du problème de franchissement des vagues au quai de Chandler, Baie des Chaleurs, Québec

1983 ◽  
Vol 10 (4) ◽  
pp. 681-694
Author(s):  
Yvon Ouellet ◽  
Marc Drouin
Keyword(s):  
Scale Model ◽  
Wave Overtopping ◽  
Model Study ◽  
The Stability ◽  
Crest Height

Wave overtopping can be tolerated in order to reduce the crest height of a structure and consequently its cost. However, if the rate of overtopping becomes too important, the resulting damage incurred on the lee side may become a problem, which has to be overcome by the addition of an appropriate structure to reduce these effects. That is what is happening at Chandler in Gaspé, Quebec, where the wharf was damaged many times, owing to wave overtopping since its construction between the years 1967 and 1971. Different ways to solve the problem have been tried without much success. A scale-model study has been carried out in order to examine the importance of this phenomenon and to compare the efficiency of different solutions suggested to attenuate its destructive effects without reducing the stability of the armor protection.Wave overtopping can be tolerated in order to reduce the crest height of a structure and consequently its cost. However, if the rate of overtopping becomes too important, the resulting damage incurred on the lee side may become a problem, which has to be overcome by the addition of an appropriate structure to reduce these effects. That is what is happening at Chandler in Gaspé, Quebec, where the wharf was damaged many times, owing to wave overtopping since its construction between the years 1967 and 1971. Different ways to solve the problem have been tried without much success. A scale-model study has been carried out in order to examine the importance of this phenomenon and to compare the efficiency of different solutions suggested to attenuate its destructive effects without reducing the stability of the armor protection.

Degradation Behavior of Poly(ethylene glycol) Diblock and Multiblock Polymers with Hydrolytically Degradable Ester Linkages

2004 ◽  
Vol 69 (8) ◽  
pp. 1643-1656 ◽  
Author(s):  
Alena Braunová ◽  
Michal Pechar ◽  
Karel Ulbrich
Keyword(s):  
Ethylene Glycol ◽  
Hydrolytic Degradation ◽  
Dicarboxylic Acids ◽  
Drug Carriers ◽  
Poly Ethylene Glycol ◽  
Model Study ◽  
Alkaline Conditions ◽  
Rate Of Hydrolysis ◽  
Poly Ethylene ◽  
The Stability

Diblock and multiblock polymers of poly(ethylene glycol) containing degradable ester bonds between the blocks were synthesized and characterized. Monofunctional poly(ethylene glycol) (PEG 2000) was modified by aliphatic dicarboxylic acids (malonic, succinic, glutaric, maleic) to obtain monocarboxylic polymers PEG-COOH containing ester bonds. Diblock polymers (4000) were prepared by polycondensation of a diamine (ethane-1,2-diamine, L-lysine) and the semitelechelic PEG-COOH. The relationship between the structure of the linkage connecting two PEG blocks and the rate of its hydrolytic degradation was studied at pH 5.5, 7.4 and 8.0. The rate of hydrolysis of all polymers was significant already under mild alkaline conditions (pH 7.4 and 8.0) and increased with increasing pH. The ester bonds of polymers with saturated dicarboxylic acid moieties were stable at pH 5.5. However, the presence of double bond in the acid moiety substantially decreased the stability of the polymer not only in alkaline but also in acid medium. The results of this model study can be utilized in the design of biodegradable high-molecular-weight drug carriers and polymers for preparation of "stealth" systems intended for therapeutic application.

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