Crucial experiment

The crucial experiments that determined the structures of a number of very simple crystals, beginning with sodium chloride, were done, not by von Laue and his helpers, but by the Braggs, William (1862-1942) and Lawrence (1890-1971), father... 

When Mitchell first described his chemiosmotic hypothesis in 1961, little evidence existed to support it, and it was met with considerable skepticism by the scientific community. Eventually, however, considerable evidence accumulated to support this model. It is now clear that the electron transport chain generates a proton gradient, and careful measurements have shown that ATP is synthesized when a pH gradient is applied to mitochondria that cannot carry out electron transport. Even more relevant is a simple but crucial experiment reported in 1974 by Efraim Racker and Walther Stoeckenius, which provided specific confirmation of the Mitchell hypothesis. In this experiment, the bovine mitochondrial ATP synthasereconstituted in simple lipid vesicles with bac-teriorhodopsin, a light-driven proton pump from Halobaeterium halobium. As shown in Eigure 21.28, upon illumination, bacteriorhodopsin pumped protons... 

The crucial experiment suggesting that the H2 molecule might act as a dihapto ligand to transition metals was the dramatic observation that toluene solutions of the deep purple coordinatively unsaturated 16-electron complexes [Mo(CO)3(PCy3)2] and [W(CO)3-(PCy3)2l (where Cy = cyclohexyl) react readily and cleanly with Ha (I atm) at low temperatures to precipitate yellow crystals of [M(CO)3H2(PCy3)2] in 85-95% yield. The... 

In Section 8.3 the mechanism of heterolytic dediazoniation of arenediazonium ions was discussed, and it was shown that the hypothesis of Crossley et al. (1940) that the aryl cation is the characteristic metastable intermediate in those reactions was not consistent with some experimental facts found in 1952 by Lewis and Hinds. Nevertheless, these facts did not have significant influence on the scientific community, which continued to accept the original and apparently convincing hypothesis of the rate-limiting formation of an aryl cation as an intermediate as correct . The incom-patabilities of various mechanistic hypotheses with experimental facts were, however, discussed in some detail only two decades later (Zollinger, 1973 a). Another year passed before I performed a crucial experiment that refuted a number of hypotheses (Bergstrom et al., 1974, 1976). ... 

It is appropriate at the beginning of a review of atomic structure to ask the question, "How do we know what we know " In other words, "What crucial experiments have been performed and what do 3... 

Heating the B-doped samples above 200°C in vacuum to dissociate the hydrogenated complex results in flat spreading resistance (Rs) at the original bulk value. A second exposure to Hj restores the increased Rs at the surface. These are crucial experiments that demonstrate that hydrogen is involved and that the process is reversible and reproducible. 

Christian Anfinsen did the crucial experiment that showed that primary structure determines tertiary structure for proteins C. J. Epstein, R. F. Goldberger, and C. B. Anfinsen, Cold Spring Harbor Symp Quant Biol 28 439 (1963). This experiment is not always as simple... 

In one of the early crucial experiments towards unravelling the reaction pathways observed, Shaw has elegantly demonstrated that in the case of ethyl and tert-butylamine reactions with N3P3CI6 the incoming nucleophile determines the type of product formed [18,53] (Eqs. 14-17)... 

The crucial experiment to identify whether this satellite structure is due to a localized 5 f hole, is claimed to be photoemission spectroscopy, in which the excitation (provided by synchrotron radiation) is tuned through the 5d-5f threshold energy . At the threshold energy an empty 5 f state just beyond Ep becomes occupied... 

As mentioned in section 4.3.3, there are two kinds of a receptor in brain and peripheral tissues. The crucial experiments have shown that brain tissue prelabeled with pH]NE will release neurotransmitter upon electrical stimulation or exposure to K+. The release is reduced by the a agonist clonidine (4.42) and stimulated by the a antagonist yohimbine (4.43). Since the adrenoreceptor involved in this latter experiment plays a vital role in modulating neurotransmitter release, it must be presynaptic and located on the nerve-ending membrane. A similar selectivity has also been shown by peripheral tissues (heart, uterus), leading to the distinction of aj (postsynaptic) and (presynaptic) adrenergic receptors. There are also presynaptic [3 receptors, which show a feedback regulation opposite to that of the ttj receptors that is, their excitation by a neurotransmitter increases NE release. 

But I think that the explanation may be quite straightforward. All we need to do is cobble together several well-established cognitive science building blocks and then do a crucial experiment. 

The crucial experiments suggesting these novel concepts were begun in the late 1960s, became fully developed in the mid-1970s, and continue to be fruitful today. 

The following crucial experiment was made ou one of the pictures. It was suspended for twelve months in the open air, under the principal chimney of the New Museum at Berlin during that time it was exposed to sunshine, mist, snow, and rain, and nevertheless retained its full brilliancy of color. 

Albert Michelson developed the interferometer about 1880 and conducted the Michelson-Morley experiment in 1887, in which it was found that the speed of light is independent of the motion of the source and the observer, this crucial experiment led Einstein to the theory of relativity. Michelson also used the interferometer to create the predecessor of today s length standard based on the wavelength of light. He received the Nobel Prize in 1907 for precision optical instruments and the spectroscopic and metrological investigations carried out with their aid. ... 

Max Planck once said, Experiments are the only means of knowing that we have at our disposal the rest is theory and imagination. How do we know. . . signals a box that introduces either a crucial experiment or experimental procedure. How do we know the distribution of molecular speeds How do we know that an electron has spin ... 

Eight years later Sagnac made a crucial experiment. The Sagnac-type experiments are broken open the complexes of concepts of relativistic light theory. Thus it became an incomplete theory since its prediction of the shift of interference is AX X - X- = 0, contrary to the Sagnac-type experiments. 

The Michelson-Morley- and Sagnac-type experiments give only two independent equations—Eqs. (13) and (15)—for three unknown hidden parameters c. c, and cp. In the present case the incompleteness means that there are three unknown parameters for two equations. A third equation is needed in the form of a crucial experiment for the unique solutions. (Of course, this crucial experiment must be independent of the M-M- and Sagnac-type experiments.) In this manner we will be able to develop an authentic nonquantized (complete) theory of light. 

In the following, three crucial experiments are described which will show the validity of the crystalline model. 

The key experiment was one which would not be carried out until Skou learned of a paper published in German four years earlier, which showed that the movement of cations across the red cell membrane was inhibited by cardiac glycosides such as ouabain, plant alkaloids used for some 200 years in the therapy of heart failure. In 1957, Skou was unaware of this important finding, and wrote later that he had not done the crucial experiment to show Na/K ATPase as the transport system. When done, the experiment was decisive ouabain inhibited the ATPase activity exactly as it did the cation fluxes. This led to a flurry of activity in many biochemical laboratories and allowed Skou (nine years after his original publication) to write a review in which he concluded that the enzyme fulfilled the requirements for a system responsible for active transport of Na+ and K+ across the cell membrane. Thus the Na/K ATPase had the following properties ... 

Thanks for enthusiastic cooperation are due to W. Hartwig, who carried out the initial crucial experiments, but also to U. Groth, H. Kehne, R. Lonsky, H.-J. Neu-bauer, J. Nozulak, K.-H. Pospischil, K.-O. Westphalen, C. Deng and Y. Chiang. 

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