Wave-Height Currents

Modelling of the hydrodynamic reaction to the activities of response resources, such as booms, skimmers and chemical dispersants was performed. The simulated processes included oil spread, evaporation, sinking in the water column, burn-off, and the pollutant s interaction with the coastline. Environmental conditions, including air temperature, wind speed and direction, wave height, current set and drift, could be adjusted dynamically during the simulation. PISCES II enables to calculate... 

To evaluate the availability performance of a skimmer, at first one needs to focus on its elements reliability performance, maintainability performance, and maintenance support performance (Barabady et al. 2010). Reliability of a system is defined as the probability that a system will perform a specified function within prescribed limits, under given environmental conditions, for a specified time (Stapelberg 2009). In other words, the failure rate of a skimmer depends on a number of parameters including environmental (operational) conditions. Low ambient temperature, wave height, current speed, sea ice concentration, and wind speed are some examples of operational conditions in the Arctic offshore. Figure 3 depicts some of the operational conditions that may affect the availability performance of the skimmers intended to be used in the Arctic offshore. 

The measurement of the current for a redox process as a fiinction of an applied potential yields a voltaimnogram characteristic of the analyte of interest. The particular features, such as peak potentials, halfwave potentials, relative peak/wave height of a voltaimnogram give qualitative infonnation about the analyte electrochemistry within the sample being studied, whilst quantitative data can also be detennined. There is a wealth of voltaimnetric teclmiques, which are linked to the fonn of potential program and mode of current measurement adopted. Potential-step and potential-sweep... 

The accuracy of the method depends upon the precision with which the two volumes of solution and the corresponding diffusion currents are measured. The material added should be contained in a medium of the same composition as the supporting electrolyte, so that the latter is not altered by the addition. The assumption is made that the wave height is a linear function of the concentration in the range of concentration employed. The best results would appear to be obtained when the wave height is about doubled by the addition of the known amount of standard solution. This procedure is sometimes referred to as spiking. 

In the controlled (constant) potential method the procedure starts and continues to work with the limiting current iu but as the ion concentration and hence its i, decreases exponentially with time, the course of the electrolysis slows down quickly and its completion lags behind therefore, one often prefers the application of a constant current. Suppose that we want to oxidize Fe(II) we consider Fig. 3.78 and apply across a Pt electrode (WE) and an auxiliary electrode (AE) an anodic current, -1, of nearly the half-wave current this means that the anodic potential (vs. an RE) starts at nearly the half-wave potential, Ei, of Fe(II) - Fe(III) (= 0.770 V), but increases with time, while the anodic wave height diminishes linearly and halfway to completion the electrolysis falls below - / after that moment the potential will suddenly increase until it attains the decomposition potential (nearly 2.4 V) of H20 -> 02. The way to prevent this from happening is to add previously a small amount of a so-called redox buffer, i.e., a reversible oxidant such as Ce(IV) with a standard... 

The analysis stage involves scanning the voltage applied to the electrode towards a more positive (anodic) potential. As the potential becomes more positive, so the metal atoms are re-oxidized, giving an anodic wave of current. The current will show a maximum value as all the atoms of a particular element are stripped off the electrode as ions. The height of the peak that results is proportional to the amount of metal and the voltage at which stripping occurs will be characteristic of the element. 

Figure 6.11 Polarogratn of a solution containing three analytes, showing three different waves . The half-wave potential, 1/2, for each is characteristic of the respective analyte couples, while the wave heights reflect the relative concentrations of each ion. The trace has been smoothed to remove the sawtoothed effects seen in Figures 6.7 and 6.8. The solution also contained KCl (0.1 mol dm ) as a swamping ionic electrolyte, and Triton X-lOO (a non-ionic surfactant) as a current maximum suppressor.

A difference in wave-heights, exploited in cases in which the difference in half-wave potentials is so small that the waves merge, can be caused either by the fact that the number of electrons consumed in the electrode reaction of the electroactive reactant differs from that involved in the electrode reaction of the electroactive product, or by a difference in the values of the diffusion coefficients of reactant and product, or by a difference in the character of the limiting current. This can occur, for example, in the case where a reactant gives a diffusion-controlled current and the product a kinetic current, or vice versa. 

Simultaneously the wave in increases, and in the final product, corresponding to a mixture of benzaldehyde and acetophenone, only waves 3 and 4 persist. The wave at intermediate stages of the reaction therefore corresponds to the reduction both of the ketol VII and of acetophenone, which is reasonable since the polarographically active benzoyl grouping is the same in both substances. To determine the ketol concentration it is necessary to subtract from wave in the current corresponding to acetophenone reduction. Since acetophenone is formed at the same concentration as benzaldehyde and because for equimolar solutions of benzaldehyde and acetophenone the ratio of wave heights iz/ii is practically equal to unity, it is possible to determine the ketol concentration simply from the difference 4 — t3. 

If the electron-transfer step in an electrode reaction is preceded by a chemical reaction that involves proton transfer, the polarographic current often will be a complex function of the concentration of the electroactive species, the hy-dronium ion concentration, and the rate constants for proton and electron transfer. Currents controlled by the rate of a chemical reaction are called kinetic currents and often are observed in the reduction of electroactive acids (e.g., pyruvic acid), in which the protonated form of the acid is more easily reduced than the anion. A polarogram of pyruvic acid in unbuffered solution exhibits two waves whose relative wave heights depend on the concentration of pyruvic acid and the solution pH.59... 

The limiting current or wave-height is usually measured at a selected potential as the difference between the current observed in the pme... 

It is very important under what conditions the dependence of mercury pressure is studied. Only under conditions when the measured current ic corresponds to not more than 15% of the total limiting current (i A + ic)> is the kinetic current virtually indepiendent of mercury pressure. The higher the current, the less characteristic the dependence on mercury pressure becomes until, when reaches the total wave height ( A + c) fi d wave ij is negligible, the current depends on the square-root of reservoir-height, as for diffusion-controlled currents. Under these conditions the transformation of A into C is fast and the wave-height is limited by the rate of the diffusion of species A. Hence, the effect of mercury pressure is imequivocal, but only when the wave Iq is small. 

Reactions that take place consecutive to the electrode process can be studied polarographioally only in those cases in which the electrode process is reversible. In these cases the wave-heights and the wave-shape remain unaffected by the chemical processes. However, the half-wave potentials are shifted relative to the equilibrium oxidation-reduction potential, determined e.g. potentiometrically. Hence, whereas in all above examples, limiting currents were measured to determine the rate constant, it is the shifts of half-wave potentials which are measured here. First- and second-order chemical reactions will be discussed in the following. 

Quantitative problems are addressed by using the limiting current values of the electrochemical reactions (wave height) to determine the total surface area, size, concentration and mass of minerals (metals) of an ore body. First consider the limiting current density, because the limiting current is the product of the limiting current density and the surface area. In the general case the current density is. 

In considering the effect of river inflows on corals in the bay, we focused on soil grains rather than salinity because the effect of low salinity due to inflows from the rivers is smaller and shorter than that of soil grains. In considering the effect of oceanic mechanical force on corals in the bay, we focused on wave height rather than tidal current because tidal full and residual currents have a smaller effect on corals than does wave height. 

Current wave height measurement data are available on the website of the Baltic Operational Oceanographic System (BOOS, see www.boos.org). 

The plateau current of a simple reversible wave is controlled by mass transfer and can be used to determine any single system parameter that affects the limiting flux of electroreactant at the electrode surface. For waves based on either the sampling of early transients or steady-state currents, the accessible parameters are the fi-value of the electrode reaction, the area of the electrode, and the diffusion coefficient and bulk concentration of the electroactive species. Certainly the most common application is to employ wave heights to determine concentrations, typically either by calibration or standard addition. The analytical application of sampled-current voltammetry is discussed more fully in Sections 7.1.3 and 7.3.6. 

---