Multiple origin concept

Although such textbook diagrams are called Lewis structures, they are not the electron-dot diagrams that G. N. Lewis originally wrote for such species. Lewis s depiction of S042-, for example, is reproduced in Fig. 3.90. This shows a normal-valent S2+ ion with shared-pair bonds to four O- ions, which is fully consistent with the octet rule, with no intrinsic need for multiple resonance structures to account for the observed Td symmetry. According to Lewis s original concept, each ion is... 

Using the original concept of ZoBell [1943], Characklis and Dryers [1992] consider the relation between cells that are "temporary" or reversibly attached and those that are irreversibly bound to the surface. Ignoring multiplication of cells at the surface an equilibrium will be established such that ... 

Unfortunately transplants require 6-7 foetal brains to obtain enough transplantable material for one patient, which itself raises ethical considerations, and as the tissue cannot diffuse its influence is restricted, even with multiple injection sites, and only a fraction (approx. 20%) of the neurons survive. Also without knowledge of the cause of PD the transplant could meet the same fate as the original neurons. The concept, however, demands perseverance and a number of variants are being tried. 

A micro reactor concept proposed by MIT and DuPont on the basis of electronic circuits is the most prominent among the examples listed for the hybrid approach [19,101]. The so-called turnkey multiple micro-reactor test station relies on the use of standard components originating from the semiconductor industry for microchemical processing, the construction being oriented at the concept of printed circuit boards. 

Neuropathic pain is defined as spontaneous pain and hypersensitivity to pain associated with damage to or pathologic changes in the peripheral nervous system as in painful diabetic peripheral neuropathy (DPN), acquired immunodeficiency syndrome (AIDS), polyneuropathy, post-herpetic neuralgia (PHN) or pain originating in the central nervous system (CNS), that which occurs with spinal cord injury, multiple sclerosis, and stroke. Functional pain, a relatively newer concept, is pain sensitivity due to an abnormal processing or function of the central nervous system in response to normal stimuli. Several conditions considered to have this abnormal sensitivity or hyperresponsiveness include fibromyalgia and irritable bowel syndrome. 

Albert H. Coons (Fig. 1.2) was the first who attached a fluorescent dye (fluorescein isocyanate) to an antibody and used this antibody to localize its respective antigen in a tissue section. The concept of putting a visible label on an antibody molecule appeared both bold and original. His initial results were described in two brief papers in the early 1940s (Coons et al. 1941,1942), but the research was halted while he joined the army and spent the next 4 years in the South Pacific. His later studies (Coons and Kaplan 1950) contributed immensely to the use of the fluorescent antibody method in a wide variety of experimental settings. In our time, the use of antibodies to detect and localize individual or multiple antigens in situ has developed into a powerful research tool in almost every field of biomedical research (http //books.nap.edu/html/biomems/acoons.pdf). 

Small molecule crystallographers are familiar with these concepts, since it is routine to measure data at low temperature to improve precision by reduction of thermal motion, and structures are often done at multiple temperatures to assess the origins of disorder in atomic positions. Albertsson et al. (1979) have reported the analysis of the crystal structure of Z)(-l-)-tartaric acid at 295, 160, 105, and 35 K. Figure 22 shows the individual isotropic. S-factors for the atoms in the structure at each of these temperatures the smooth variation of B with T is apparent. Below 105 K, B is essentially identical for all atoms and is also temperature independent the value of B = 0.7 agrees well with the expected zero-point vibradonal value. However, even for this simple structure, not all of the atoms show B vs T behavior at high temperature which extrapolates to 0 A at 0 K. 

The bond length data, although not satisfactory, do suggest that the P—C bond has multiple character with a bond order of about 2. Other physical measurements which support this and provide further insight are detailed below. Note that many of the original studies which reported these data discuss them in terms of dn-pn overlap on the basis that it is evidence for such overlap. Since the d orbital concept is now discarded, these discussions are obsolete, but the experimental results still give useful information. 

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