Classic Experiments

Land and McCann (1971) then developed a computational theory for color constancy, the retinex theory. In their experiments, they used a stimulus similar to the famous paintings 

With this experiment, Land and McCann vividly demonstrated that the perceived color of an object does not depend on the light reflected by the object. The perceived color depends on the reflectance, which specifies how much of the incident light is reflected. The reflectance determines the color of the object. The reflected light is essentially proportional to the product of the irradiance (see Table B.l for a definition) and the reflectance of the object. A human observer is somehow able to derive the reflectances for the objects in view regardless of the illuminant used. In contrast, a digital or an analog camera can do no more than the telescopic photometer can. It only measures the reflected light. In order 

To see if the environment has an impact on the perceived color, Land and McCann also moved the rectangular patches around on the Mondrian. They report that the color sensation does not change significantly if the rectangle is moved to a new neighborhood where it is surrounded by different colored rectangles. 

Land and McCann (1971) came to the conclusion that color perception involves structures of the retina as well as the visual cortex. On the basis of these experiments, Land and McCann developed a computational theory of color constancy, the retinex theory. Land later developed additional versions of his retinex theory. The retinex theory of color vision is discussed in detail in Chapter 7. 

---

The Exclusion Prin cip le is t ii an tn ni mechanical in nature, and outside the realm ofeveryday, classical" experience. Think ofii as iheinherent tendency of electron s to slay away from oneanoiher, to be m n tnally excluded. Excbi sion is due to lb c an lisymmdry of the wave function and nol to electrostatic coulomb repulsion between two electrons. Exclusion exists even m the absence of electrostatic repulsions. 

The classical experiment tracks the off-gas composition as a function of temperature at fixed residence time and oxidant level. Treating feed disappearance as first order, the pre-exponential factor and activation energy, E, in the Arrhenius expression (eq. 35) can be obtained. These studies tend to confirm large activation energies typical of the bond mpture mechanism assumed earlier. However, an accelerating effect of the oxidant is also evident in some results, so that the thermal mpture mechanism probably overestimates the time requirement by as much as several orders of magnitude (39). Measurements at several levels of oxidant concentration are useful for determining how important it is to maintain spatial uniformity of oxidant concentration in the incinerator. 

The classic experiments of Von Meting and Minkowski in 1889 first impHcated the pancreas in regulating blood glucose levels removal of a dog s pancreas led directly to the development of hyperglycemia. Then in the early 1920s it was shown that an internal secretion of the pancreas could be isolated... 

The simple form of time derivative of concentration was used in classical experiments in physical chemistry to express the rate of reaction. This must be changed to satisfy the condition in industrial reactors in which many other physical changes, such as flow and diffusion occur and for which conditions are frequently in a transient state. These forms are reviewed here. 

Up to this point in our discussion, we have considered only carbocations in which the cationic carbon can be 5p -hybridized and planar. When this hybridization cannot be achieved, die carbocations are of higher energy. In a classic experiment, Bartlett and Knox demonstrated that the tertiary chloride 1-chloroapocamphane was inert to nucleophilic substitution. Starting material was recovered unchanged even after refluxing for 48 h in ethanolic silver nitrate. The umeactivity of this compound is attributed to the structure of... 

S. Murad, J. G. Powles. A computer simulation of the classic experiment on osmosis and osmotic pressure. J Chem Phys 99 7271, 1993. 

In a classic experiment, Edward Hughes (a colleague of Ingold s at University College, London) studied the rate of racemization of 2-iodooctane by sodium iodide in acetone and compared it with the rate of incorporation of radioactive iodine into 2-iodooctane. 

MnOi- He called the gas vitriol air and reported that it was colourless, odourless and tasteless, and supported combustion better than common air, but the results did not appear until 1777 because of his publisher s negligence. Priestley s classic experiment of using a burning glass to calcine HgO confined in a cylinder inverted over liquid mercury was first performed in Colne, England, on 1 August 1774 he related this to A. L. Lavoisier and others at a dinner party... 

This important fact was first demonstrated by Vernon in a series of classical experiments, some of which are summarised graphically in Fig. 3.1. He showed that rusting is minimal in pure air of less than 100 l o relative humidity but that in the presence of minute concentrations of impurities, such as sulphur dioxide, serious rusting can occur without visible precipitation of moisture once the relative humidity of the air rises above a critical and comparatively low value. This value depends to some extent upon the nature of the atmospheric pollution, but, when sulphur dioxide is present, it is in the region of 70-80%. Below the critical humidity, rusting is inappreciable, even in polluted air. 

What strategy should one follow In the classical experiment, one factor is varied at a time, usually over several levels, and a functional relationship between experimental response and factor level is established. The data analysis is carried out after the experiment(s). If several factors are at work, this approach is successful only if they are more or less independent, that is, do not strongly interact. The number of experiments can be sharply increased as in the brute-force approach, but this might be prohibitively expensive if a single production-scale experiment costs five- or six-digit dollar sums. Figure 3.4 explains the problem for the two-factor case. 

Nasmyth There is a classic experiment to address whether there is size control. That is to transiently delay the cell cycle so that you produce abnormally large cells. Then you look at the cell division time of subsequent cycles. If these experiments are done with bacteria or yeast, the subsequent cycles are greatly accelerated. These experiments could be done by Bruce Edgar and his imaginal discs. They are technically harder, but they could be done. 

The concept of chemical neurotransmission originated in the 1920s with the classic experiments of Otto Loewi (which were themselves inspired by a dream), who demonstrated that by transferring the ventricular fluid of a stimulated frog heart onto an unstimulated frog heart he could reproduce the effects of a (parasympathetic) nerve stimulus on the unstimulated heart (Loewi Navratil, 1926). Subsequently, it was found that acetylcholine was the neurotransmitter released from these parasympathetic nerve fibers. As well as playing a critical role in synaptic transmission in the autonomic nervous system and at vertebrate neuromuscular junctions (Dale, 1935), acetylcholine plays a central role in the control of wakefulness and REM sleep. Some have even gone as far as to call acetylcholine a neurotransmitter correlate of consciousness (Perry et al., 1999). 

In 1883, Osborn Reynolds conducted a classical experiment, illustrated in Fig. 6-1, in which he measured the pressure drop as a function of flow rate for water in a tube. He found that at low flow rates the pressure drop was directly proportional to the flow rate, but as the flow rate was increased a point was reached where the relation was no longer linear and the noise or scatter in the data increased considerably. At still higher flow rates the data became more reproducible, but the relationship between pressure drop and flow rate became almost quadratic instead of linear. 

In a classic experiment that was conducted for decades in general chemistry laboratories, oxygen can be prepared by the decomposition of KC103 in the presence of Mn02. 

Figure 2. The differential enthalpy of Ca 2K exchange (d(AHx/dx) as a function of fractional K saturation for the Batcombe series soils from various plots of the Broadbalk Classical Experiment at Rothamsted. 

This last method, it is interesting to note, was employed by Amagat for the preparation of the hydrogen for his classic experiments on the relationship of pressure to volume... 

---