Experimental artifacts

An example of interaction stiffness and force curves for a Si surface with a native oxide at 60% relative humidity (RH) is shown in Fig. 12 [104]. The stiffness and force data show an adhesive interaction between the tip and substrate. The hysteresis on retraction is due to a real change in contact area from surface oxide deformation and is not an experimental artifact. The adhesive force observed during retraction was consistent with capillary condensation and the surface energy measured from the adhesive force was close to that of water. 

In order to eliminate the possibility that the observed FRC signal was due to diffusion effects or other experimental artifacts, two types of blank runs were performed with each catalyst. In one set of experiments, Ife was used as the "adsorbing" gas with a reduced catalyst while in a second set, H2 was used with a non-reduced catalyst. Neither type or experimental led to any observable FRC signal. 

Unfortunately the development of models is hindered by a lack of reliable experimental data. For example, the rates of ion-transfer reactions measured at different times and by different groups vary widely. Also, it has been suggested that the high interfacial capacities that are measured in certain systems are an experimental artifact [13]. While this is frustrating for the researcher who wants to decide between competing models, it can also be viewed as a sign that the electrochemistry of liquid-liquid interfaces is an active field, where fundamental issues are just being explored. 

Franck and Hertz (1913) first demonstrated that an electron has to acquire a minimum energy before it can ionize. Thus, they provided an operational definition of the ionization potential and showed that it is an atomic or molecular property quite free from experimental artifacts. However, this kind of experiment does not tell anything about the nature of the positive ion for this, one needs a mass spectrometric analysis. Although Thompson had demonstrated the existence of H+, H2+, and H3+ in hydrogen discharge, it seems that Dempster (1916) was the first to make a systematic study of the positive ions. 

Munson, P. J. (1983). Experimental artifacts and the analysis of ligand binding data results of a computer simulation, J. Receptor Res., 3, 249-259. 

Figure 4.1. Relative luminescence quantum yield (a) and absorption spectrum of Ru(bpyh2+ in methanol at room temperature (b, c) (7), The decline in luminescence yields at the extremes are experimental artifacts. (Reprinted from Ref. 10 with permission, Copyright 1971 American Chemical Society.)...

Hysteresis may be caused by experimental artifacts or degradation. Also, to assess hysteresis fairly from the desorptive direction requires that samples be at true equilibrium. 

Of course, experimental artifacts should be avoided. In particular, in mechanistic electroorganic work these are... 

As we have seen in the previous sections, our understanding of SOFC cathode mechanisms often hinges on interpretation on the magnitude and time scale of electrochemical characteristics. However, these characteristics are often strongly influenced by factors that have nothing to do with the electrode reaction itself but rather the setup of the experiment. In this section we point out two commonly observed effects that can potentially lead to experimental artifacts in electrochemical measurements (1) polarization resistance caused gas-phase diffusion and (2) artifacts related to the cell geometry. As we will... 

Genuine (true) and apparent hysteresis may be considered to explain contaminant release from the subsurface solid phase. Genuine hysteresis assumes that observed data are real and the equilibrium results can be explained on the basis of well-identified phenomena. Apparent hysteresis results from an experimental artifact due, for example, to a failure to reach retention or release equilibrium. 

Some confusion about toluene ion dissociation thermochemistry has arisen from the PEPICO rate-energy curve reported by Bombach, R. Dannacher, J. Stadelmann, J.-T. J. Am. Chem. Soc. 1983,105,4205, which is not in agreement with other observations and apparently suffered from an experimental artifact. The two-charmel analysis offered in their paper was qualitatively but not quantitatively correct See Refs. 5, 19. 

In the ESI MS studies some care must be taken due to the possible formation of false peaks (73). The time-of-flight (TOF) ESI MS equipment of a new generation with an orthogonal interface design allows one to avoid somewhat experimental artifacts of this kind. 

It must be emphasized again that the mid-peak potential is equal to E° for a simple, reversible redox reaction when neither any experimental artifact nor kinetic effect (ohmic drop effect, capacitive current, adsorption side reactions, etc.) occurs, and macroscopic inlaid disc electrodes are used, that is, the thickness of the diffusion layer is much higher than that of the diameter of the electrode. 

The Van Deemter equation remained the established equation for describing the peak dispersion that took place in a packed column until about 1961. However, when experimental data that was measured at high linear mobile phase velocities was fitted to the Van Deemter equation it was found that there was often very poor agreement. In retrospect, this poor agreement between theory and experiment was probably due more to the presence of experimental artifacts, such as those caused by extra column dispersion, large detector sensor and detector electronic time constants etc. than the inadequacies of th Van Deemter equation. Nevertheless, it was this poor agreement between theory and experiment, that provoked a number of workers in the field to develop alternative HETP equations in the hope that a more exact relationship between HETP and linear mobile phase velocity could be obtained that would be compatible with experimental data. 

So we end this section with unanswered questions Do the unusual scattering matrices measured by the Russian investigators really exist in nature, or are they merely experimental artifacts If the former, how is this reconciled with the measurements of Thompson et al. ... 

The structure-sensitive reactions present a more serious problem. First, one must always make sure that the observed sensitivity is not an experimental artifact. Then when the sensitivity is established reliably, it is not always easy to rationalize it. 

The least resolved measurement is determination of the isothermal rate constant k(T), where T is the isothermal temperature. Although conceptually simple, such measurements are often exceedingly difficult to perform for activated process without experimental artifact (contamination) because they require high pressures to achieve isothermal conditions. For dissociative adsorption, k(T) = kcol (T) [S (Tg = TS = T)), where kcol(T) is simply the collision rate with the surface and is readily obtainable from kinetic theory and Tg and T, are the gas and surface temperatures, respectively [107]. (S ) refers to thermal averaging. A simple Arrhenius treatment gives the effective activation energy Ea for the kinetic rate as... 

Another kind of wall-effect was proposed by El perin (1967). He suggested that an adsorbed layer of polymer molecules could exist at the pipe wall during flow and this could lower the viscosity, create a slip, dampen turbulence pulsations, and prevent any initiation of vortices at the wall. Later work (Little 1969), however, with a transparent pipe and dyed polymer, showed that the adsorption could in be fact an experimental artifact (a quantity of polymer solution, trapped in pressure gage piping, slowly diffused back into the solvent flow). Although polymer molecules do more or less adhere to clean surfaces in thin films, there is no interaction with the bulk of the solution which could alter the flow properties (Gyr, 1974). Thus, it is evident that adsorption of the additives on surfaces is not the reason for the drag reducing effect. 

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