Differentiation between artifacts

Other recent investigations involving AES, often with depth profiling, deal with the surface segregation of Ag in Al-4.2 % Ag [2.163], of Sn in Cu and formation of superficial Sn-Cu alloy [2.164], of Mg in Al-Mg alloy [2.165], and of Sb in Ee-4% Sb alloy [2.166]. Note the need to differentiate between, particularly, segregation, i. e. original sample properties, from the artifact of preferential sputtering. 

A serious problem associated with quadrature detection is that we rely on the cancellation of unwanted components from two signals that have been detected through different parts of the hardware. This cancellation works properly only if the signals from the two channels are exactly equal and their phases differ from each other by exactly 90°. Since this is practically impossible with absolute efficiency, some so-called image peaks occasionally appear in the center of the spectrum. How can you differentiate between genuine signals and image peaks that arise as artifacts of quadrature detection ... 

It is noteworthy that in the study of A. cocke relli (Smith etal, 2009), synthetic n-alkanes were used, while in other studies usually branched or unsaturated alkanes were synthesized. However, standard synthesis of such compounds leads to a mixture of stereoisomers. If social insects can differentiate between these stereoisomers, bioassays with such synthetic compounds may lead to artifacts. An important future goal is to assess the importance of such stereoisomers and test the respective natural form in the bioassays. 

Differences in chemical compositions usually provide new information about artifacts. By differentiating between the sources of the raw materials used to produce objects, it is possible to infer cultural contacts. For some artifacts, detailed studies of compositional differences can also help us understand production methods. The remains of the humans themselves may also be analyzed to provide useful information. The contributions that chemists have made in the study of archaeological materials have gone far beyond the simple chemical analysis of the materials. This volume gives but a small part of the great contributions that chemists have made toward the understanding of ancient materials and technologies. 

In Chapter 2, Hancock, Pavlish, and Sheppard give an example of a case in which visual examination of stone tools was not adequate to differentiate between lithic artifacts that were produced from rocks that were very different in their origins. During the Mesolithic and early Neolithic times, the inhabitants of what is now Portugal used a variety of materials. Although most of the stone tools were classified by the archaeologists as sedimentary cherts, Hancock concluded that many tools were made of volcanic rhyolite. 

The main efforts in the early period were directed toward demonstrating that the incorporation observed with the slices could be validly related to results obtained in the whole animal. One of the approaches used was a comparison of the initial rates of incorporation in the slices with those observed in vivo. Despite the many artifacts, i.e., incorporation of labeled amino acids into other than peptide bonds [for a detailed discussion of these see Tarver (15)], it had been amply demonstrated by 1950 [for review of the evidence see Borsook (SO)] that on the whole, the rate of protein synthesis in slices or minces and in some metabolically active cell suspensions was very comparable to the rates in the corresponding organ in situ. This is in sharp contrast, as we shall see, with the situation in homogenates or otherwise damaged cells—hence the choice in this chapter of speaking of whole cells rather than differentiating between a tissue outside or inside the animal. 

The second approach is based on heat loss rather than solar gain. The saturated roof sections are better heat conductors (poorer insulators) than the dry sections. The temperature difference between the interior and exterior will cause heat to flow more through the wet sections than the dry sections. Consequently, warmer areas on the exterior surface indicate water saturation. Of course, since there is a temperature differential between the interior and exterior, this approach is more subject to artifacts caused by air flow and thermal conduction through the roof The appearance of the thermograms is otherwise quite similar. 

Ideally an image restoration technique will deliver an image that is consistent with available data and constraints (e.g., positivity), and which is free of obvious artifacts. Any technique that achieves this should be taken seriously, regardless of whether it is based on an ad hoc procedure or justified by a formalism such as maximum entropy. It is the data, ultimately, that must drive a restoration process. In analyzing the solution to any ill-posed problem, it is important to differentiate between those characteristics dicatated by the data, and those that are dependent on the solution technique. Any physically implausible feature that is not required by the data should be ignored. 

We noted that Equation 4.77 is very important in the nonisothermal operation of a CSTR. This algebraic equation has more than one solution and leads to the concept of multiple steady states (MSS). On the other hand, the differential equation that characterizes a PER has only one solution, that is, the PER operates at a single steady state. Multiple steady states are of particular concern to us because they can occur in the physically realizable range of variables, between zero and infinity, and not at absurd values such as negative concentration or temperature (which would then be no more than a mathematical artifact). 

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