Phenomenon Topics

Calcium channel blockers (CCBs) are the most widely used pharmacologic agents for the treatment of peripheral vasospasm (110-112). Sympatholytic agents have also been used in the treatment of Raynaud s phenomenon. Topical nitroglycerin ointment can be applied with a nocturnal nitrate-free interval to avoid nitrate tolerance. 

Before proceeding to the main subject of this chapter—namely, the behavior and properties of spread films on liquid substrates—it is of interest to consider the somewhat wider topic of the spreading of a substance on a liquid surface. Certain general statements can be made as to whether spreading will occur, and the phenomenon itself is of some interest. 

Resonance Raman Spectroscopy. If the excitation wavelength is chosen to correspond to an absorption maximum of the species being studied, a 10 —10 enhancement of the Raman scatter of the chromophore is observed. This effect is called resonance enhancement or resonance Raman (RR) spectroscopy. There are several mechanisms to explain this phenomenon, the most common of which is Franck-Condon enhancement. In this case, a band intensity is enhanced if some component of the vibrational motion is along one of the directions in which the molecule expands in the electronic excited state. The intensity is roughly proportional to the distortion of the molecule along this axis. RR spectroscopy has been an important biochemical tool, and it may have industrial uses in some areas of pigment chemistry. Two biological appHcations include the deterrnination of helix transitions of deoxyribonucleic acid (DNA) (18), and the elucidation of several peptide stmctures (19). A review of topics in this area has been pubHshed (20). 

Curie chose for her dissertation research the new topic of uranium rays, a phenomenon that had only recently been observed by Henri Becqiierel. The mystery was the source of the energy that allowed uranium salts to expose even covered photographic plates. Curie s first efforts in the field were systematic examinations of numerous salts to determine which salts might emit rays similar to those of Becquerel s uranium. After discovering that both thorium and uranium were sources of this radiation. Curie proposed the term radioactive to replace uranium rays. She also discovered that the intensity of the emissions depended not on the chemical... 

There remains one topic to be discussed in our survey of chemical bonding in organic compounds. For most compounds, all the molecules have the same structure, whether or not this structure can be satisfactorily represented by a Lewis formula. But for many other compounds there is a mixture of two or more structurally distinct compounds that are in rapid equilibrium. When this phenomenon, called tauto-merism, exists, there is a rapid shift back and forth among the molecules. In most cases, it is a proton that shifts from one atom of a molecule to another. 

The investigation of chiral molecular phenomena, and associated technique development, thus hnds potentially signihcant practical applications to place alongside the fundamental interest of this topic. This chapter will examine the recently investigated phenomenon of photoelectron circular dichroism (PECD) that arises from a dissymmetry in the angular distribution of photoelectrons... 

While on the topic on electrical conduction and resistance offered by an electrically conducting medium it is usual to extend to a phenomenon called superconductivity this has now been recognized as having a profound impact on the electrical field. Exciting possibilities exist. The phenomenon is exhibited by certain types of matter and is characterized by two fundamental properties ... 

Uneven distributions of residuals. The MaxEnt calculations in presence of an overall chi-square constraint suffer from highly non-uniform distributions of residuals, first reported and discussed by Jauch and Palmer [29, 30] the error accumulates on a few strong reflexions at low-resolution. The phenomenon is only partially cured by devising an ad hoc weighting scheme [20,31, 32]. Carvalho et al. have discussed this topic, and suggested that the recourse to as many constraints as degrees of freedom would cure the problem [33]. 

A final point on this phenomenon - nitrogen can sometimes act as a chiral centre. This topic is explored in some detail in Section 6.6.6. 

This topic is dealt with in detail in the chapter by Real et al. In exploring other terminal N,N-chelating ligands in the [(NCX)2(N,N)Fe( -bpym)Fe(N,N) (NCX)2] system we obtained the hitherto unknown 1,10-phen complex [Fe(l,10-phen)(NCS)2]2( -bpym) [54], albeit without a crystal structure, a common phenomenon in this dinuclear series [7]. Magnetic studies (Fig. 1)... 

Studied in both an experimental and theoretical manner. The link between glycolytic oscillations and the pulsatile secretion of insulin in pancreatic p cells [53] is another topic of current concern. Models for the latter phenomenon rely on the coupling between intracellular metabolic oscillations and an ionic mechanism generating action potentials. Such coupling results in bursting oscillations of the membrane potential, which are known to accompany insulin secretion in these cells [54, 55]. 

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