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Oscillatory Behavior (oscillatory + behavior)

Distribution by Scientific Domains

Chemistry	42%

Selected Abstracts

Spontaneous Current Oscillations during Hard Anodization of Aluminum under Potentiostatic Conditions

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Woo Lee
Abstract Nanoporous anodic aluminum oxide is prepared by hard anodization of aluminum under potentiostatic conditions using 0.3,M H2C2O4. Under unstirred electrolyte condition, spontaneous current oscillations are observed. The amplitude and period of these current oscillations are observed to increase with anodization time. As a consequence of the oscillatory behavior, the resulting anodic alumina exhibits modulated pore structures, in which the diameter contrast and the length of pore modulation increase with the amplitude and the period of current oscillations, respectively, and the current peak profile determines the internal geometry of oxide nanopores. The mechanism responsible for the oscillatory behavior is suggested to be a diffusion-controlled anodic oxidation of aluminum. [source]

Time continuity in cohesive finite element modeling

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003
Katerina D. Papoulia
Abstract We introduce the notion of time continuity for the analysis of cohesive zone interface finite element models. We focus on ,initially rigid' models in which an interface is inactive until the traction across it reaches a critical level. We argue that methods in this class are time discontinuous, unless special provision is made for the opposite. Time discontinuity leads to pitfalls in numerical implementations: oscillatory behavior, non-convergence in time and dependence on nonphysical regularization parameters. These problems arise at least partly from the attempt to extend uniaxial traction,displacement relationships to multiaxial loading. We also argue that any formulation of a time-continuous functional traction,displacement cohesive model entails encoding the value of the traction components at incipient softening into the model. We exhibit an example of such a model. Most of our numerical experiments concern explicit dynamics. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A numerical study of combustion stability in emergency oxygen generators

AICHE JOURNAL, Issue 4 2006
Victor Diakov
Abstract Combustion in sodium chlorate based emergency oxygen generators is accompanied by significant oscillations of the product oxygen flow rate, which decrease the efficiency of these devices. Reactant melting and convective heat transfer from the generated gas are key steps in the process. In this work, the effect of reactant melting on filtration combustion front propagation stability in gas generating mixtures is investigated numerically. The formation of melting regions is demonstrated in cases with significant convective gas-to-core heat transfer. Numerical simulations exhibit the oscillatory behavior of oxygen generation. By decreasing the effective heat of reaction, reactant melting is detrimental to combustion front stability. The simulations show growth of pulsations with increasing reaction activation energy and decreasing convective heat transfer. A strong stabilization of front propagation is observed when combustion temperature reaches the melting point of reaction product. These results identify the important factors responsible for pulsating behavior of chemical oxygen generators. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

Study of oscillatory behavior of open-circuit potential of silicon immersed in CuSO4/HF solutions

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005
V. Parkhutik
Abstract This work studies the influence of experimental conditions on the occurrence and development of oscillations of the open-circuit potential (OCP) of silicon immersed in aqueous solution of 0.01 M CuSO4 + 0.06 M HF. The oscillations are very regular and last for days without any tendency to diminish. We show that they are quite sensitive to the temperature of the electrolyte, its viscosity, stirring, relative concentration of components, etc. We also present a phenomenological model to explain the oscillatory OCP behavior. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Parameter oscillation attenuation and mechanism exploration for continuous VHG ethanol fermentation

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009
F.W. Bai
Abstract A bioreactor system composed of a stirred tank and three tubular bioreactors in series was established, and continuous ethanol fermentation was carried out using a general Saccharomyces cerevisiae strain and a very high gravity medium containing 280 g,L,1 glucose, supplemented with 5 g,L,1 yeast extract and 3 g,L,1 peptone. Sustainable oscillations of glucose, ethanol, and biomass were observed when the tank was operated at the dilution rate of 0.027 h,1, which significantly affected ethanol fermentation performance of the system. After the tubular bioreactors were packed with 1/2, Intalox ceramic saddles, the oscillations were attenuated and quasi-steady states were achieved. Residence time distributions were studied for the packed bioreactors by the step input response technique using xylose as a tracer, which was added into the medium at a concentration of 20 g,L,1, indicating that the backmixing alleviation assumed for the packed tubular bioreactors could not be established, and its contribution to the oscillation attenuation could not be verified. Furthermore, the role of the packing's yeast cell immobilization in the oscillation attenuation was investigated by packing the tubular bioreactors with packings with significant difference in yeast cell immobilization effects, and the experimental results revealed that only the Intalox ceramic saddles and wood chips with moderate yeast cell immobilization effects could attenuate the oscillations, and correspondingly, improved the ethanol fermentation performance of the system, while the porous polyurethane particles with good yeast cell immobilization effect could not. And the viability analysis for the immobilized yeast cells illustrated that the extremely lower yeast cell viability within the tubular bioreactors packed with the porous polyurethane particles could be the reason for their inefficiency, while the yeast cells loosely immobilized onto the surfaces of the Intalox ceramic saddles and wood chips could be renewed during the fermentation, guaranteeing their viability and making them more efficient in attenuating the oscillations. The packing Raschig rings without yeast cell immobilization effect did not affect the oscillatory behavior of the tubular bioreactors, further supporting the role of the yeast cell immobilization in the oscillation attenuation. Biotechnol. Bioeng. 2009;102: 113,121. © 2008 Wiley Periodicals, Inc. [source]

Dynamical Complexity in Electrochemical Oxidations of Thiocyanate

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2009
Li LIU
Abstract Kinetics and mechanism of the electrochemical oxidation of thiocyanate on a Pt electrode were investigated by using various electrochemical methods, in which both current and potential oscillations have been observed. Cyclic voltammetry measurements illustrate that the oxidation process consists of two steps. In addition to the oscillatory behavior, the system also exhibits bistability, in which the oxidation could be switched between a high and a low current density states with a temporal potential perturbation. The presence of inert ions with stronger absorption also induces transitions from oscillatory to steady reactions in the thiocyanate system. [source]

A study of the relation between current oscillations and pitting

CHINESE JOURNAL OF CHEMISTRY, Issue 10 2003
Hou-Yi Ma
Abstract Anodic polarization behaviors of iron in pure H2SO4 and three mixed acidic solutions, H2SO4 + NaCl, H2SO4 + NaNO3 and H2SO4+ NaCl + NaNO3, were investigated. The potentiodynamic sweep curves showed that the current densities rose and dropped irregularly in H2SO4 + NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H2SO4 + NaCl solution and only a few unobvious corrosion spots were observed in H2SO4 + NaCl + NaNO3 solution after the iron electrode was potentiostatically polarized at 1.3 V. The oscillatory properties of iron are associated with the susceptibility of the iron to pitting. In H2SO4 + NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irregular current fluctuations due to occurrence of the pitting; whereas in H2SO4 + NaCl + NaNO3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H2SO4 solution. Thus, when the higher the oscillatory frequency, the more irregular oscillatory process and the more sensitive to pitting iron occurred. [source]