Reality, sense

At the other end of the spectrum are the ab initio ( from first principles ) methods, such as the calculations already discussed for H2 in Chapter 4. I am not trying to imply that these calculations are correct in any strict sense, although we would hope that the results would bear some relation to reality. An ab initio HF calculation of the potential energy curve for a diatomic Aj will generally give incorrect dissociation products, and so cannot possibly be right in the absolute sense. The phrase ab initio simply means that we have started with a certain Hamiltonian and a set of basis functions, and then done all the intermediate calculations with full rigour and no appeal to experiment. 

We issue a mild caution. One must always be mindful of the temptation to see things not as they really are but only how they appear to be at the moment using whatever happens to be the most convenient or accepted way of looking at things. This is the dreaded solution in search of a problem phenomenon, disguised, in the case of physicists trying to make sense of the world, as the temptation to use whatever is the latest fad or theory simultaneously as a lens and litmus test for reality. 

It-from-bit embodies the central notion that every it - that is, every aspect of reality electrons, protons, photons, fields of force, or even the what we call space-time itself - is in the deepest sense a derivative of experimentally deduced answers to yes/no questions that is, to bits. If we allow ourselves for a moment to go back to the roots of what it is that we by convention call reality, we see that it is something that is literally defined by a particular sequence of yes/no responses elicited from either a mechanical or (our own biological) sensory apparatus in other words, reality s origin is fundamentally information-theoretic. 

Reality Check Note that although molecular formulas give the composition of the molecule, they reveal nothing about the way the atoms fit together. In that sense they are less useful than structural formulas. 

Reality Check This value is reasonable in the sense that lowering the temperature should reduce the vapor pressure. 

Reality Check Notice that moving from left to right, one en replaces two OH- ions. This makes sense an en molecule has two lone pairs that can bond to the metal OH-has only one. 

Many of the examples end with a Reality Check, which encourages you to check whether the answer makes sense. We hope you will get into the habit of doing this when you work problems on your own in quizzes and examinations. 

What I hope to have added to the discussion has been a philosophical reflection on the nature of the concept of element and in particular an emphasis on elements in the sense of basic substances rather than just simple substances. The view of elements as basic substances, is one with a long history. The term is due to Fritz Paneth, the prominent twentieth century radio-chemist. This sense of the term element refers to the underlying reality that supports element-hood or is prior to the more familiar sense of an element as a simple substance. Elements as basic substances are said to have no properties as such although they act as the bearers of properties. I suppose one can think of it as a substratum for the elements. Moreover, as Paneth and before him Mendeleev among others stressed, it is elements as basic substances rather than as simple substances that are summarized by the periodic table of the elements. This notion can easily be appreciated when it is realized that carbon, for example, occurs in three main allotropes of diamond, graphite and buckminsterfullenes. But the element carbon, which takes its place in the periodic system, is none of these three simple substances but the more abstract concept of carbon as a basic substance. 

It is often asked whether or not the constituent structures of a resonating system, such as the Kekul4 structures for the benzene molecule, are to be considered as having reality. There is one sense in which this question may be answered in the affirmative but the answer is definitely negative if the usual chemical significance is attributed to the structures. A substance showing resonance between two or more valence-bond structures does not contain molecules with the configurations and properties usually associated with these structures. The constituent structures of the resonance hybrid do not have reality in this sense. 

The problem we face is that we have to estimate a wavefront, which has an infinite number of degrees of freedom, from a finite number of measurements. At first this may seem impossible, but in reality an infinite range of possible solutions describes most practical situations, not just wavefront sensing. The key to solving the problem is that we need to make an assumption about the relative likelihood of the solutions. As an example of how this is done, consider a wavefront sensor which makes a single measurement that is sensitive to only two basis functions. 

One can only wonder what sense some students make of the instruction that the reality involves eight electrorrs distributed over the three C-0 bonds that is, 2 /3 electrorrs per bond, or each bond equivalent to IV3 classical two-electron bonds ... 

Common teaching experience suggests that sometimes students sense-making operates on representations, rather than on the sub-microscopic reality that they rep-... 

The consequence of all these (conscious and unconscious) simplifications and eliminations might be that some information not present in the process will be included in the model. Conversely, some phenomena occurring in reality are not accounted for in the model. The adjustable parameters in such simplified models will compensate for inadequacy of the model and will not be the true physical coefficients. Accordingly, the usefulness of the model will be limited and risk at scale-up will not be completely eliminated. In general, in mathematical modelling of chemical processes two principles should always be kept in mind. The first was formulated by G.E.P. Box of Wisconsin All models are wrong, some of them are useful . As far as the choice of the best of wrong models is concerned, words of S.M. Wheeler of New York are worthwhile to keep in mind The best model is the simplest one that works . This is usually the model that fits the experimental data well in the statistical sense and contains the smallest number of parameters. The problem at scale-up, however, is that we do not know which of the models works in a full-scale unit until a plant is on stream. 

In the early days of CHEMFET development, the expectations for successful application to a variety of biomedically important sensing applications were high. This was in part due to the fact that CHEMFET s are easily miniaturized (<2 mm surface area) and so are obvious candidates for in vivo applications. This enthusiasm has largely been tempered by the reality that although field-effect tran-... 

The term model-based can be a source of confusion because descriptions of any aspects of reality can be considered to be models. Any KBS is model based in this sense. For some time, researchers in KBS approaches (Venkatasubramanian and Rich, 1988 Finch and Kramer, 1988 Kramer and Mah, 1994 McDowell and Davis, 1991,1992) have been using model-based to refer to systems that rely on models of the processes that are the objects of the intent of the system. This section will avoid confusion by using the term model to refer to the type of model in which the device under consideration is described largely in terms of components, relations between components, and some sort of behavioral descriptions of components (Chandrasekaran, 1991). In other words, model-based is synonymous with device-centered. Figure 27 shows a diagram displaying relationships among components. The bubble shows a local model associated with one of the components that relates input-output relationships for flow, temperature, and composition. 

Harpur, Patrick. Daimonic reality a field guide to the other world. Viking, 1994 reprint, London, New York Arkana, 1995. xxi, 330 p. ISBN 0-14-019485-1 "Mysterious lights in the sky, phantom animals, visions of the Virgin Mary, UFO s, fairies, alien abductions Daimonic Reality makes sense of these apparitions and... 

Another answer is that you just need to know the things on the exam. Later ends at the final. In reality, later may be longer than this. Try to pick out the major concepts of biochemistry as you go along. Concepts are generally easier to remember than factual details—particularly if the concepts make sense. 

Fig. 21 (a) Rectification in the AR sense electron transfers occur first between electrode MD and the HOMO of the D-o-A molecule (1 ), and between the LUMO and MA (1), thus establishing the zwitterionic excited state D+-a-A , which then (2) relaxes back into the neutral state, (b) Rectification in the anti-AR sense if auto-ionization occurs first (1), forming the excited state D+-a-A by an interaction of the intense electric field and the molecule, followed by transfers to and from the electrodes (2) and (2 ), resulting in the electron passing from MD to MA. The molecular energy levels, which in reality must perforce shift dramatically during the electron transfer process, are drawn here for simplicity as if the molecule were still isolated in the gas phase ... 

In the broadest sense, of course, no model is unique (see, for example, Oreskes et al., 1994). A geochemical modeler could conceptualize the problem differently, choose a different compilation of thermodynamic data, include more or fewer species and minerals in the calculation, or employ a different method of estimating activity coefficients. The modeler might allow a mineral to form at equilibrium with the fluid or require it to precipitate according to any of a number of published kinetic rate laws and rate constants, and so on. Since a model is a simplified version of reality that is useful as a tool (Chapter 2), it follows that there is no correct model, only a model that is most useful for a given purpose. 

---