Thickness Of Compact Layer Research Articles

The effect of an electrical double layer on the voltammetric performance of nanoscaleinterdigitated electrodes: a simulation study

Finite-element based computational simulation is performed to investigate the effect of anelectrical double layer (EDL) on the electrochemical processes of nanometer-scaleinterdigitated electrodes (nano-IDEs). Results show that the EDL structure will alter thevoltammetric current response of nano-IDEs due to the expansion of the diffuse layer intothe diffusion layer at the electrode surfaces and the overlap of the electrical fields of theneighboring electrodes. The EDL induced change in the voltammetric current response ismore severe for nano-IDEs with a smaller electrode size and gap spacing, and theEDL effect is influenced by the compact layer thickness, the charge valence ofthe redox species, the electron transfer rate, and the absence of the supportingelectrolyte.

Behaviour of Subgrade Soil Reinforced with Geogrid

The beneficial effects of reinforcing subgrade soils with a single layer of geogrid and their behaviour under static and cyclic loading are investigated. Three types of soil and two types of geogrid varying in their stiffness were selected. CBR, static triaxial and unconfined compression tests were conducted by reinforcing the samples at different depths within the sample height. The optimum position was decided based upon the CBR value, the modulus of elasticity (E-value), and deviator stress at failure. Cyclic triaxial tests were conducted for unreinforced specimens as well as reinforced specimens at the deduced optimum position of the geogrid to study their behavior under repetitive loads. The results showed that CBR and E-values increase with reinforcement and attain the highest values when geogrid is placed at a depth between 72 and 76% from top of the specimen. Height of specimen in laboratory for all practical purposes means thickness of compacted layer of subgrade soil in the field. The results of cyclic triaxial tests indicated that the resilient strain in unreinforced soil samples decreased by almost 35% with geogrid reinforcement. Further, geogrids can play an important role in the control of the rut formation in the pavement system as the permanent strain in reinforced samples decreased by 44% of that in unreinforced samples.

Influence of self-affine roughness on Parsons-Zobel plots for electrical double layers

In this paper we investigate the dependence of Parsons-Zobel plots on characteristic self-affine roughness parameters of the metal electrode in electrical double layers. Among the roughness amplitude w, the correlation length xi, and roughness exponent H, the latter appears to have the most prominent effect especially for values in the range H<0.5. In addition, with decreasing compact layer thickness the influence of roughness leads to stronger nonlinear behavior of the plots for relatively large electrode potentials. Finally, it is shown that dynamic changes of the electrode roughness (for example by growth on metal films) should be carefully quantified with respect to their influence on the Parson-Zobel plots and related double-layer systems.

Pacing-induced ventricular remodeling in the chick embryonic heart.

Chronic ectopic pacing in the adult heart induces myocardial hypotrophy close to the pacing site. We have recently described a similar localized decrease of compact myocardium thickness in the chick embryonic heart after 48 h of intermittent apical ventricular pacing. Here we analyze the cellular mechanisms underlying the response of the embryonic heart to pacing. Because the developing heart had been found to adjust its morphology according to functional demands by undergoing cellular hyperplasia or hypoplasia, we hypothesized that the stimulation should result in hypoplasia of the apical ventricular compartment. Morphologic analysis of hearts submitted to 18 h of effective pacing during 48 h showed a mild to moderate ventricular dilatation, a 28% decrease in the apical compact layer thickness with no changes in other ventricular locations, and atrial wall thickening. These modifications were caused by changes in the number of cell layers, whereas cell size was similar between paced and control hearts. Analysis of proliferative activity after 24 h of pacing showed a decrease of 32% in the rate of cell proliferation limited to the apical compact layer exposed to stimulation. No ultrastructural injury or increased cell death was found. These changes were accompanied by down-regulation of the myocardial growth factor fibroblast growth factor-2 but no differences were found in the expression of platelet-derived growth factor. Thus, chronic intermittent ventricular pacing induces myocardial remodeling in the chick embryonic heart, on the basis of locally regulated rates of cell proliferation.

A quantitative study of the ventricular myoarchitecture in the stage 21-29 chick embryo following decreased loading.

During the early developmental period, ventricular myoarchitecture undergoes a transition from a smooth-walled cardiac tube, to left and right ventricular chambers filled with a sponge-like network of trabecular struts. We measured the quantitative changes of ventricular myocardium properties in normal stage 21-29 chick embryos and after chronic verapamil suffusion, which is known to decrease work load and decelerate ventricular growth. The morphologic parameters (compact layer thickness, ventricular wall composition, porosity of different layers and trabecular orientation) were determined from scanning electron micrographs of transversely dissected perfusion-fixed hearts. A vascular bed of stage 21 chick embryos was suffused with 1 ng of verapamil at 1 microliter per hour up to stages 24, 27 and 29 via a miniosmotic pump. From stage 24, the thickness of the compact myocardium in the left ventricle was greater than that of the right. The increase in thickness was minimal between stages 24 and 27, while the predominantly radially arranged trabeculae comprised up to 75% to total myocardial mass. The ratio of intertrabecular spaces to trabeculae (local porosity) decreased form the ventricular center (70%) towards the compact myocardium (0%). In verapamil-treated embryos, the hearts were smaller and showed delayed development. The compact myocardium was thinner than normal, and the proportion of trabeculae was higher than in controls. The local porosity values were similar in control and experimental groups. Decreased load resulted in delayed growth and morphogenesis, expressed as persistence of trabeculae and a thinner compact myocardium. Embryonic heart pumping function is largely based on extensively developed trabeculation with regionally different properties.

Internal Friction/Attenuation in a β‐Spodumene Glass‐Ceramic

Transient creep and attenuation (internal friction) of a β‐spodumene glass‐ceramic has been examined. Four‐point flexural creep tests have been performed at high tempera‐ture(T = 925°‐1000°C) and modest stress levels (σl,max= 7‐25 MPa). The flexural creep response of the glass‐ceramic is characterized by a large decelerating transient that precedes the establishment of a steady state. The creep response is transformed via a numerical algorithm to give the attenuation spectrum. In addition, low‐stress (2.5‐30 MPa), subresonant‐frequency (10 −5 Hz ≤ f ≤ 1 Hz), com‐pression‐compression attenuation experiments have been performed. A first‐order thermodynamic analysis of the effect of effective pressure on the volume fraction of re‐sidual glass suggests that the dilatational process that is associated with the flexural deformation mode should be characterized by a single loss mechanism. The predictions that are available from the flexural creep tests, as well as those that have been directly measured in experiments, in‐dicate that attenuation behavior is insensitive to both fre‐quency and temperature and exhibits a characteristic band of absorption. The weak frequency dependence of this an‐elastic response is well‐characterized by a power law of the form Q−1χfα, where 0.15 ≥ a ≥ 0.3, which suggests a physical mechanism that possesses a distribution of relax‐ation times. A plausible explanation exists in the fluid‐mechanics description of deformation‐induced melt migra‐tion, in which the crystalline β‐spodumene “matrix” undergoes compaction or dilatation while the residual glass phase, which forms an interpenetrative network along grain triple junctions of the matrix, flows: the evolution with time of the compacted (and/or dilated) layer thickness of the deforming matrix produces a distribution of compli‐ances.

On the inhibitory effect of normal aliphatic alcohols upon Cd 2+, Pb(OH) −3 and Bi 3+ electroreductions on mercury at high surface coverages

A detailed investigation of the inhibitory effect of normal aliphatic alcohols, from n-butanol to n-octanol, upon Cd 2+ and Bi 3+ reductions and Cd o (Hg) oxidation in perchloric medium, as well as upon Pb(OH) − 3 reduction and Pb o (Hg) oxidation in (NaF + NaOH) mixtures, was carried out at different ionic strengths on dropping mercury and amalgam electrodes. Experiments were conducted under conditions in which the coverage θ of the electrode surface by the surface-active alcohols is almost complete (θ ≅ 1). The experimental values of the ratio (k θ=1/k θ=0) of the rate constant for the electrode reaction at high surface coverages to the corresponding rate constant in the absence of the alcohols, were compared with a theoretical expression of the form [1] ▪ Here c * s and C * W are the bulk concentrations of the alcohol(S) and of water (W), n ≠ and n S are the numbers of adsorbed water molecules displaced from the electrode surface by one adsorbing particle of the activated complex for the electrode reaction (≠) and by one adsorbing molecule of the surfactant S, respectively, and Δ G o ads is the standard free energy of adsorption of S. Moreover, c is the coordination number in the adsorbed monolayer and Δ G lat measures the energy involved in the process ▪ where the hyphen denotes lateral interactions between contiguous particles in the adsorbed monolayer. The derivation of eqn. (1) relies on the following assumptions: ( i) the activated complex for the electrode reaction is specifically adsorbed and is the same independent of whether it is formed by displacement of adsorbed solvent molecules or of adsorbed surfactant molecules; ( ii) the theory of absolute reaction rates applies; ( iii) the surfactant is adsorbed under equilibrium conditions. The expression for Δ G lat depends both on the particular model of the adsorbed monolayer and on the particular mechanical statistical treatment of this model. For all systems investigated the quantity (cn ≠ Δ G lat/RT) turns out to be notably positive. This behaviour can be explained by the ability of adsorbed water molecules to establish strong ion-dipole interactions - and, possibly, further interactions of a more specific nature - with the charged activated complex, no such strong interactions with this complex being established by adsorbed aliphatic molecules. The experimental dependence of k θ=1 for Pb(OH) − 3 and Bi 3+ reduction and for Pb o (Hg) oxidation upon the bulk concentration of n-butanol, under certain experimental conditions, suggests a gradual passage from the mechanism previously outlined to an alternative mechanism in which the rate determining step involves the tunnelling of the transferring electron for the Me(II) + e ⇌ Me(I) charge transfer step, across the adsorbed monolayer of the alcohol. This gradual passage takes place as the n-butanol bulk concentration is progressively decreased. The dependence of the rate constant k θ=1, suitably corrected for diffuse-layer effects, upon the applied potential in the presence of the various normal aliphatic alcohols, is in qualitative agreement with an expression which accounts for the progressive increase in the compact-layer thickness with an increase in the length of the hydrocarbon chain.

Electrode kinetics, equivalent circuits, and system characterization: Small-signal conditions

The small-signal steady-state response around the point of zero charge of an electrode/material system is examined for an unsupported electrolyte (material) with two species of charge carrier of arbitrary mobilities and valence numbers and with arbitrary intrinsic/extrinsic conduction character, taking full account of bulk, electrode reaction, sequential adsorption, and diffusion processes. The exact solution of the transport equations of the problem for generalized Chang-Jaffé single-point boundary conditions is compared with the responses of a variety of plausible equivalent circuits, using a complex least squares fitting technique. A hierarchical circuit is found which closely reproduces the exact results when charge of one sign is completely blocked without adsorption, except for some of the cases in which diffusion and reaction effects interfere with each other. The circuit is composed of frequency-independent lumped capacitances and resistances separately identified with bulk, reaction, and adsorption/reaction processes and a single, finite-length, Warburg-like impedance for diffusion effects. Relations between the circuit elements and microscopic electrode/material parameters are found and apply irrespective of the time-frequency overlap between bulk, reaction, and adsorption processes. It is also found that the reaction and adsorption resistances and the adsorption capacitance are all strongly interrelated. The circuit may be used with simultaneous non-linear least squares fitting of the real and imaginary parts of experimental impedance data to obtain estimates of the values of circuit elements and thus of the values of the microscopic parameters characterizing the electrode/material system. The relationship of small-signal response for overpotential-dependent electrode kinetics to that obtained for Chang-Jaffé boundary conditions is then considered. The reaction resistance and adsorption capacitance are found to be formally identical for Butler-Volmer (or Butler-Volmer-like) and Chang-Jaffé conditions. In the d.c. limit these quantities are unchanged, for the boundary conditions just mentioned, when a supporting electrolyte is added. A transformation of variables method is described which permits one to determine the smallsignal impedance of an electrode/material system with general overpotential-dependent firstorder electrode reaction kinetics from a compact-layer model for the small-signal overpotential and the small-signal response obtained for Chang-Jaffé boundary conditions. Exact impedance results are given for the case of a single species of mobile charge carrier. Analysis of this case indicates that the overpotential dependence of the boundary conditions has negligible effect on the small-signal response unless the cell is of microscopic thickness or the Debye length is comparable to the compact layer thickness and the electrode reaction is slow.