Energetic Condition Research Articles

The Effects of Surface Energetics on the Cyclic Voltammetry of Metallocenes at Nonilluminated n ‐ InP Electrodes

Electron transfer processes at n‐type electrodes of moderate to low doping density were investigated by monitoring the cyclic voltammetric dark currents of a series of metallocenes in acetonitrile solutions. The formal reduction potentials of the metallocenes span the bandgap of , allowing a comparison of the cyclic voltammetric response as a function of the formal reduction potential and the energetic condition of the electrode surface. The energetic condition of the electrode surface during the cyclic voltammetry experiments was monitored by measurements of the capacitance of the space charge region. A simple chemical etching and electrochemical cycling procedure yielded reproducible surface energetics. The interface in the depletion condition responded ideally to changes in electrode potential, as evidenced by linear Mott‐Schottky plots, over a range of about 0.9V. It was possible to achieve an accumulation condition at negative potentials, but the interface could not be inverted at positive potentials. The interface is less susceptible to surface oxidation than is the interface. For each metallocene couple, the reversibility of cyclic voltammetric (CV) waves at was dependent on the doping density of the electrode and the proximity of the formal reduction potential to the conduction bandedge . Couples with located negative of displayed nearly reversible CV waves. Couples with located in the bandgap were reduced irreversibly at overvoltages of 400–500 mV. A couple with located slightly positive of yielded a partially reversible CV wave at moderate , but the wave became irreversible at low . Oxidation of couples with positive of −0.5V vs. for ferricenium/ferrocene was not observed.

The Effects of Surface Energetics and Surface Oxide Layers on the Cyclic Voltammetry of Metallocenes at Nonilluminated p ‐ InP Electrodes

Electron‐transfer processes at highly doped electrodes were investigated by monitoring the cyclic voltammetric dark currents of a series of metallocenes in acetonitrile solutions. The formal reduction potentials of the metallocenes span the bandgap of , allowing a comparison of the cyclic voltammetric response as a function of the formal reduction potential and the energetic condition of the electrode surface. Since the electron transfer of all of the metallocenes was electrochemically reversible on the timescale of cyclic voltammetry at a platinum electrode, differences in the voltammetric responses at were attributed to processes within the semiconductor or to surface phenomena. The energetic condition of the electrode surface during the cyclic voltammetric experiments was monitored by measurements of the capacitance of the space‐charge region. Although a simple chemical etching and electrochemical cycling procedure yielded reproducible surface energetics, the interface responded ideally to changes in electrode potential over a range of only about 0.8V. Metallocene redox couples with located within that range exhibited reversible cyclic voltammetry when the experiment was performed within that range. The couples with located outside of the ideal range displayed irreversible cyclic voltammetry. Voltammetric responses for electrodes with different crystal orientations and doping densities were compared.

Close correlation between platelet responses and adenylate energy charge during transient substrate depletion

The relation between availability of metabolic energy and thrombin-induced platelet aggregation and secretion was investigated in a system of transient substrate depletion followed by restoration of ATP resynthesis. Substrate depletion induced a fall in the concentration of metabolic ATP and in the adenylate energy charge and a concurrent decline in aggregation and secretion of dense and α-granule contents. Restoration of energy generation completely restored the adenylate energy charge and restored aggregation and secretion, but led to incomplete recovery of the ATP concentration. A close correlation between the adenylate energy charge and aggregation and between the adenylate energy charge and the secretion of dense and α-granule contents could be demonstrated. No such correlation existed between these responses and the concentration of ATP. These results show that the adenylate energy charge monitors an energetic condition which is crucial for preservation of platelet aggregation and secretion of dense and α-granule contents.

Microscopical significance of the critical characteristics of stimuli in excitation processes, as revealed by spectral analysis

We performed a spectral analysis of stimuli in the excitation process namely for three types of stimuli: rectangular pulses, sinusoidal and ramp stimuli. (a) In the case of short pulse stimuli the energetic condition imposed by membrane is more severe than for rheobasic pulse stimuli. The duration of the pulse stimuli of rheobasic intensity is optimized by the cell in such a way that an optimal spectral covering of the noise membrane is reached. (b) Membrane processes the sinusoidal stimulus so that both the energetic condition at low frequency is met and the spectral covering (which even in a liminal case must be between 0 and 200–300 Hz) is secured. (c) The spectrum of a liminal ramp signal appears to surpass that of I K noise and partly cover that of I Na noise. Our analysis shows that for modeling the threshold function of excitable nerve membrane it is necessary to satisfy: (a) the energetic condition at low frequencies and (b) the condition of spectral covering. On the basis of the model suggested by us one can make a number of predictions verifiable through experimental data among which we consider as the most important: (a) the slope of a ramp signal which if used in voltage clamps measurements gives the characteristic I Na– V and I K − V; (b) the optimal frequency in the pararesonance phenomenon.

Analysis of pairwise dislocation interaction and its contribution to flow stress during magnesium crystal basal slip

The paper reports an analysis of conditions favouring reactions during attractive interaction between basal dislocations and basal with prismatic dislocations, based on the energy gain approximation. α coefficients are calculated which relate the flow stress to the secondary basal and prismatic dislocation density. The contribution to flow stress due to these types of dislocation interactions is determined by the energetic condition of the particular reactions. Calculated values of α are compared to experimental values.

The Post Glacial Evolution of the Minas Basin, N.S. A Sedimentological Interpretation

ABSTRACT Geophysical and vibrocore information was used to interpret the distribution, character and evolution of post-glacial sediments in the Minas Basin, Bay of Fundy. Sedimentological evidence provided information on the environment of deposition of the sediments found. Results show that the Minas Basin seabed has not been subaerially exposed since glacial times and that deposition has taken place under continuously marine conditions. During the approximate period 8,600 years B.P.-6,300 years B.P. the Minas Basin was non-tidal and sedimentation occurred predominantly in the deeper parts of the embayment. From 6300 Y.B.P. to the present tidal activity has been increasing linearly; the present tidal activity is the most energetic condition to have occurred in the system. During this period d position was progressively more predominant in the marginal regions, developing the sandflats, mudflats and salt marshes visible today. The progressive inundation of the Minas Basin margins is a function of an increase in tidal range (50%) and a rise in apparent mean sea-level (50%).

Deformability and strength of soils in calculation of high earth dams

1. In the wake of other investigators, experimental investigations once again have shown that the strength of a soil depends to a considerable extent on the load trajectory, which can be characterized by the parameters λ, μ, and angle of rotation of the smooth planes α. The effect mainly of the parameter λ and to a lesser degree μ was investigated experimentally. As a result the limit surface was obtained for the case δ=5 kgf/cm2, which has a sixfold symmetry and six singular points. The curve of the limit surface between these points is convex. 2. A check of the energetic strength condition on loamy sand and clay for positive values of μ and different values of λ showed its fulfillment and the possibility of realization when solving the problem on a computer. This was shown earlier for coarse-fragmental soils. 3. A check of the energetic model of soil [1] made it possible to introduce certain corrections when describing the behavior of soil near the point of uniform compression. The refined soil model reflects well the deformability in the deviatoric stage of loading. This soil model was realized when solving the problem of the stress and strain of earth dams. 4. Dilatancy is a property of nonlinearly deformable materials and can be described by deformability parameters on the section of uniform compression and distortion, but to accelerate the computation when realizing the soil model it is convenient to use an empirical formula. 5. The refined soil model presented in the article permits taking into account such conditions as divergence in the position of the planes of principal stresses and strains and load trajectory, given in an implicit form in terms of the stagewise character of construction, limiting state, and unloading, which occurs in the upstream shoulder upon a rise of water in the upper pool.

On alternative activation mechanisms in electron-transfer reactions in solution

The model for electron-transfer kinetics in solution is considered. In one model the appropriate energetic condition for charge transfer is met by a small number of vibration-rotation states in thermal equilibrium with the solution. Collisional activation (CA) between ion in the solution and the solvent is the origin of such states. In another model CA is neglected and the appropriate energy states are regarded as being reached by the fluctuations in the energy of the ion, as a result of its interaction with many surrounding solvent molecules; this is the energy fluctuation (EF) model. The dependence of the charge-transfer rate upon the interfacial potential difference for the two models is outlined, and the differences between the models is discussed. Comparison with spectroscopic data for H3O+ in solution suggests that the energy distribution in the vibration-rotation levels in this ion is continuous and the classical modes of vibration exist in water. A supposed discontinuity, which would have annulled...

Measurement of the ion energy distribution resulting from the turbulent heating of a plasma

Measurements are reported of the ion energy spectrum of a turbulently-heated hydrogen plasma in the Cornell THM-2 experiment. The results show that the ion-heating mechanism simultaneously affects the entire length of the plasma column. Ion heating scales linearly with current, but the dependence on electric field strength is less than linear. The stored energy which drives the heating pulse is variable from 250 to 1000J. In all cases the ions account for approximately 10 percent of the total plasma energy. The efficiency of energy transfer to the plasma is approximately 4 percent, but for the most energetic condition the efficiency is found to be sensitive to the conductivity of the initially cold plasma. The H1+ energy spectrum sampled from the outer periphery of the plasma was measured during the first approximately 10 mu sec. During this time the energy spectrum is isotropic and well approximated by a two-temperature Maxwellian distribution. For the most energetic discharge the low energy component accounts for approximately 90 per cent of the ions and has Ti approximately=320 eV. The high energy component has Ti=1400 eV.

Generalization of an Energetic Optimality Condition for Nonconservative Systems

ABSTRACT An optimality condition based on strain energy densities, derived by earlier investigators, has been generalized. The generalized condition for an optimum structure is in bilinear form. The concept of the adjoint system is utilized. The resulting condition is applied to the minimization of the mass of a column loaded by a tangential follower force. Some results are presented.