Fronts and stationary domains during electrochemical H2 oxidation on Pt: The impact of the position of the reference electrode on the spatiotemporal behaviour

We studied the local potential distribution in front of a rotating Pt ring-electrode during hydrogen oxidation in sulfuric acid for three different positions of the reference electrode. The potential distribution was measured with a potential micro-probe. The experiments were carried out in the bistable region of the system. For large and medium distances between the reference (RE) and the working electrode (WE), transitions between the two homogeneous states occurred through nucleation and growth of the globally stable state from the initially metastable one. The transition time was considerably longer for the intermediate distance between the RE and the WE. For the closest distance used, stationary patterns formed, consisting of two domains with high and low current densities, respectively. The difference in the double layer potential of the two domains amounted to more than 1 V. The low-current density domain was covered with Pt-O whereas in the high current density domain the electrode surface consisted of 'bare' Pt. The existence of these stationary non-equilibrium structures as well as the difference of the front behaviour for the other two electrode arrangements can be traced back to the existence of a negative global coupling for intermediate and close distances between the WE and the RE

Bifurcation to Traveling Spots in Reaction-Diffusion Systems

A bifurcation leading to the onset of translational motion of localized particlelike structures (spots) in two-dimensional excitable media with long-range inhibition and global coupling is analytically and numerically investigated. Properties of slowly traveling spots and effects of collisions between these objects are studied

Physical Acoustics

Contains reports on two research projects.U. S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-001

Tuning the range of spatial coupling in electrochemical systems: From local via nonlocal to global coupling

A specific feature of pattern formation in electrochemical systems is the occurrence of accelerated fronts; they can be attributed to long-range spatial coupling. In this paper we demonstrate that different coupling functions can be realized by tuning easily accessible parameters: The range of the coupling crucially depends on the length scales of the system, and the strength of the coupling is proportional to the conductivity of the electrolyte. Simulations in the bistable regime are presented which illustrate how the front behavior changes qualitatively when length scales or conductivity are varied

Pattern formation in stiff oscillatory media with nonlocal coupling: A numerical study of the hydrogen oxidation reaction on Pt electrodes in the presence of poisons

The impact of the strength of negative (desynchronizing) global coupling (NGC) on the spatiotemporal dynamics of an electrochemical relaxation oscillator is studied numerically with a prototypical model, the electro-oxidation of hydrogen in the presence of poisons. The results are compared with recent experiments. The NGC has a destabilizing effect on the homogeneous oscillations. Both, in theory and in experiments, the basic patterns found with increasing global coupling strength are modulated oscillations, target patterns (including an asymmetric variant), and modulated pulses, the average spatial inhomogeneity during an oscillation increasing with the intensity of the NGC. It is suggested that this scenario is typical for strong relaxation oscillations, and a comparison with an electrochemical oscillator exhibiting harmonic oscillations points to the fact that the critical coupling strength, upon which the complete synchronization is destroyed, is larger for relaxation oscillations than for harmonic oscillations. In addition, the numerical simulations predicted two- and three-phase cluster patterns at high coupling strength. Also in experiments cluster patterns were observed, however only in parameter regions of the local dynamics which were different from the one investigated in this study

The role of adsorbate–adsorbate interactions in the rate oscillations in catalytic CO oxidation on Pd (110)

The CO+O2 reaction on Pd(110) exhibits kinetic oscillations above pO2 ≊ 10−3 Torr and bistability below this pressure. Based on the reversible formation of subsurface oxygen and the Langmuir Hinshelwood mechanism of catalytic CO oxidation, a mathematical model had been developed which described the occurrence of rate oscillations and most of the qualitative features of the oscillations. This model, however, failed to reproduce the change from bistability to oscillatory behaviour with increasing pO2. In this paper we demonstrate that by introducing repulsive interactions between COad and Oad, the subsurface oxygen model correctly reproduces the experimentally determined stability diagram in pO2,pCO parameter space. The effect of the repulsive interactions is to reduce the activation barrier for penetration of chemisorbed oxygen into the subsurface region, thus facilitating the formation of subsurface oxygen at high coverages. For the improved subsurface oxygen model a bifurcation analysis has been conducted in pO2,pCO parameter space. The influence of the constants in the model has been analyzed likewise with bifurcation theory

Examining relations between psychopathology and psychopathy dimensions among adolescent female and male offenders

Aim: This study was performed to investigate relations between psychopathology and psychopathy in adolescent female and male detainees. Method: We examined 91 male and 123 female adolescent detainees (aged 14–19) for psychopathology -using the Youth Self Report, the Overt Aggression Scale-Modified and a Conduct Disorder Self Report Scale- and for psychopathic dimensions using the psychopathy checklist youth version (PCL:YV). Based on a linear regression analysis we compared the specific associations between psychopathology and psychopathy in both male and female delinquent juveniles. Results: Our results revealed higher scores for externalizing behavior and psychopathic dimensions in delinquent males, and higher internalizing problem scores in delinquent females. Furthermore, we found a positive relationship between suicidal behavior and the psychopathy total score as well as the affective, the lifestyle and the antisocial dimension only in girls. No association was found for suicidal behavior in boys. Regarding anxious-depressive behavior, we found a negative relation to the psychopathy total score and to the affective psychopathy factor for the boys. Conclusion: Expectedly, the population of incarcerated adolescents exhibited a high prevalence of psychopathology. At the same time our results referred to meaningful gender-related differences with respect to associations with psychopathy. The gender-related differences in psychopathological symptoms could indicate varied subtypes of psychopathy in boys and girls

Physical Acoustics

Contains reports on four research projects.Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E)U.S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-001

Physical Acoustics

Contains research objectives and reports on two research projects.U. S. Navy (Office of Naval Research) under Contract N00014-67-A-0204-0019Joint Services Electronics Program (Contract DAAB07-71-C -0300

Interpretation of biomechanical simulations of normal and chaotic vocal fold oscillations with empirical eigenfunctions

Empirical orthogonal eigenfunctions are extracted from biomechanical simulations of normal and chaotic vocal fold oscillations. For normal phonation, two dominant empirical eigenfunctions capture the vibration patterns of the folds and exhibit a 1:1 entrainment. The eigenfunctions show some correspondence to theoretical low‐order normal modes of a simplified, three‐dimensional elastic continuum, and to the normal modes of a linearized two‐mass model. The eigenfunctions also facilitate a physical interpretation of energy transfer mechanisms in vocal fold dynamics. Subharmonic regimes and chaotic oscillations are observed during simulations of a lax cover, in which case at least three empirical eigenfunctions are necessary to capture the resulting vocal fold oscillations. These chaotic oscillations might be understood in terms of a desynchronization of a few of the low‐order modes, and may be related to mechanisms of creaky voice or vocal fry. Furthermore, some of the empirical eigenfunctions captured during complex oscillations correspond to higher‐order normal modes described in earlier theoretical work. The empirical eigenfunctions may also be useful in the design of lower‐order models (valid over the range for which the empirical eigenfunctions remain more or less constant), and may help facilitate bifurcation analyses of the biomechanical simulation