Fundamental aspects

The complex phenomena associated with the interaction of ionizing radiation with diverse liquids and solids, addressed in detail elsewhere in this book, are relevant and applicable to irradiated chilled or frozen foods. Specific influences of the food composition and structure directly affect the nature and reaction of the resulting free radicals formed [1]. Irradiation parameters and conditions further affect the reaction pathways of the radicals and the yield of stable products derived from them [2, 3]. 

Although the primary radicals formed in the sarcoplasmic fluid of the muscle tissue, in the myofibrillar proteins of the muscles, and in the lipids of the intercellular and depot fats are expected to be similar to those formed in dilute aqueous solutions, in polypeptides, and in meat triglycerides, respectively, the radical yields and reactivities are affected by density and solute concentration 

As a consequence of competitive pathways for radical reactions, the yield of a particular radiolysis product depends on the accumulated dose and dose rate. 

If the precursor of the product is the major constituent and the product does not react with other radicals, then its yield will be linear. In some instances, a product with high reactivity toward primary radicals is formed, resulting eventually in a steady-state level of that product and in a delayed linear increase in an associated secondary product. If the precursor is a minor constituent, then the yield of the product will increase initially with dose and then level off when the precursor is depleted. The different possible yield-dose relationships and their implications for extrapolating data are discussed in earlier work [5]. 

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

The success of fluorescent sensors can be explained by the distinct advantages offered by fluorescence detection in terms of sensitivity, selectivity, response time, local observation (e.g. by fluorescence imaging spectroscopy). Moreover, remote sensing is possible by using optical fibers. The great improvement in the sensitivity 

Another distinction should be made (independently of the fluorescence aspects) between chemical sensors (also called chemosensors) and biosensors. In the former, the analyte-responsive moiety is of abiotic origin, whereas it is a biological macromolecule (e.g. protein) in the latter. 

In fluorescent molecular sensors, the fluorophore is the signaling species, i.e. it acts as a signal transducer that converts the information (presence of an analyte) into an optical signal expressed as the changes in the photophysical characteristics of the fluorophore. In contrast, in an electrochemical sensor, the information is converted into an electrical signal. 

CEF Chelation or Complexation Enhancement of Fluorescence CEQ Chelation or Complexation Enhancement of Quenching Fig. 10.1. Main classes of fluorescent molecular sensors of ions or molecules. 

The discovery of crown ethers and cryptands in the late sixties opened new possibilities of cation recognition with improvement of selectivity, especially for alkali metal ions for which there is a lack of selective chelators. Then, the idea of coupling these ionophores to chromophores or fluorophores, leading to so-called chromoionophores and fluoroionophores, respectively, emerged some years later l9) As only fluorescent probes are considered in this chapter, chromoionophores will not be described. 

In the design of a fluoroionophore, much attention is to be paid to the characteristics of the ionophore moiety and to the expected changes in fluorescence characteristics of the fluorophore moiety on binding. The complexing ability of the ionophore will be considered first. 

Stability (or binding) constants Ks are often used instead of dissociation constants (Ks = 1/Kd). These equilibrium constants are concentration quotients as the corresponding activity coefficients are given the value 1. However, in many practical situations, other 

Fluorescent signaling receptors of cations are generally classed according to the nature of the cation to be probed, but in this chapter devoted to the principles of design, they will be classed according to the involved photophysical processes. 

Chemical Composition. With few exceptions, inorganic pigments are oxides, sulfides, oxide hydroxides, silicates, sulfates, or carbonates (see Tables 3 and 4), and normally consist of single-component particles (e.g., red iron oxide, a-Fe203) with well defined crystal structures. However, mixed and substrate pigments consist of nonuniform or multicomponent particles. 

In the case of substrate pigments, at least one additional component (pigment or extender) is deposited onto a substrate (pigment or extender), preferably by a wet method. Weak, medium, or strong attractive forces develop between these pigment 

Chemical class White pigments Black pigments 

Oxides titanium dioxide iron oxide black 

Carbon and carbonates white lead carbon black 

Adsorption to the silver surface is one of the most important requirements for a sensitizing dye. Intimate contact with the silver surface facilitates electron transfer. To make stable films with predictable photographic properties it is also 

The dyes must also have appropriate redox properties to function properly as sensitizers. If the dyes are oxidized too readily in the ground state, silver atoms can be prematurely and unselectively reduced, and this causes photographic fog. Fog is the unwanted, indiscriminate reduction of silver. Photographic fog causes a loss of signal-to-noise ratio and degrades image quality. The redox potentials of sensitizing dyes have also been extensively measured and correlated to performance [15], 

When a photon enters a pigmented film, one of three events may occur  

It may simply pass through the film (the binder being assumed to be nonabsorbent) 

Colorimetry relates the perceived color quaUty to the color stimulus, which in turn is based on the reflectance spectrum p(2,). 

The Kuhelka-Munk theory relates p X) to scattering, absorption, and film thickness (scattering coefficient S, absorption coefficient K, film thickness h). 

The theory of multiple scattering (scattering interaction) relates the scattering coefficient S to the pigment volume concentration a and to the scattering diameter Qg of the individual particle. The absorption coefficient K is directly proportional to the absorption diameter and the concentration a. 

Class 1 fluorophores that undergo quenching upon collision with an analyte (e.g. O2, C1-). 

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Comprehensive coverage of all fundamental aspects of Fourier transform infrared spectroscopy. 

Szymanski S, Gryff-Keller A M and Binsch G A 1986 Liouville space formulation of Wangsness-Bloch-Redfield theory of nuclear spin irelaxation suitable for machine computation. I. Fundamental aspects J. Magn. Reson. 68 399-432... 

Shores D A, Rapp R A and Flou P Y (eds) 1997 Proc. Symp. on Fundamental Aspects of High Temperature Corrosion vol 96-26 (Pennington, NJ Electrochemical Society)... 

Engel T 1996 Fundamental aspects of the reaction of thermal and hyperthermal F, F2, Cl, and CI2 with Si surfaces Japan. J. Appl. Phys. 35 2403-9... 

X-ray Photoelectron Spectroscopy. X-ray photoelectron spectroscopy (xps) and Auger electron spectroscopy (aes) are related techniques (19) that are initiated with the same fundamental event, the stimulated ejection of an electron from a surface. The fundamental aspects of these techniques will be discussed separately, but since the instmmental needs required to perform such methods are similar, xps and aes instmmentation will be discussed together. 

R. A. Buchanan and E. E. Stansbury, "Aqueous Corrosion", in R. Kossowsky, ed., Suface Modfcation Engineering Fundamental Aspects, CRC Press, Boca Raton, Fla., 1989. 

The first demonstration of catalytic conversion of synthesis gas to hydrocarbons was accompHshed ia 1902 usiag a nickel catalyst (42). The fundamental research and process development on the catalytic reduction of carbon monoxide was carried out by Fischer, Tropsch, and Pichler (43). Whereas the chemistry of the Fischer-Tropsch synthesis is complex, generalized stoichiometric relationships are often used to represent the fundamental aspects ... 

The scientific interests of Anatoly K. Babko ranged widely, especially in regard to fundamental aspects of analytical chemistry, applications of organic reagents in inorganic analysis, chemistry of complex compounds (including heteropolyacids), analytical applications of complex compounds in photometry, luminescence and chemiluminescence, ion chromatography, and liquid-liquid extraction. 

The one-dimensional geometry of a radially expanding ring is perhaps the simplest for considering fundamental aspects of the fracture and fragmentation process. In a ductile metal ring, fracture proceeds through the multiple... 

Computational methods have played an exceedingly important role in understanding the fundamental aspects of shock compression and in solving complex shock-wave problems. Major advances in the numerical algorithms used for solving dynamic problems, coupled with the tremendous increase in computational capabilities, have made many problems tractable that only a few years ago could not have been solved. It is now possible to perform two-dimensional molecular dynamics simulations with a high degree of accuracy, and three-dimensional problems can also be solved with moderate accuracy. 

Effects of transport processes cannot be ignored in investigations aimed at more fundamental aspects of kinetics and catalysis. The interaction of chemical and physical processes was noticed a long time ago. M. V. Lomonosov mentioned in 1745 ... 

In this chapter we shall illustrate some fundamental aspects of enzyme catalysis using as an example the serine proteinases, a group of enzymes that hydrolyze peptide bonds in proteins. We also examine how the transition state is stabilized in this particular case. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

We have attempted to relate the basics of silicone chemistry to applications where adhesion is an important property. These applications cover a vast industrial arena that does not make a review of this sort easy. Instead, we focused on the fundamental aspects of silicone physics and chemistry and related them to adhesion and adherence properties. We have attempted to use a logical structure to help the reader understand silicone adhesion. Adhesion and cohesion have been considered as they both determine the ultimate performance of an adhesive joint. 

Staehle, R. W. Comments on the History of Engineering and Science of Stress Corrosion Cracking, in Proc. Fundamental Aspects of Stress Corrosion Cracking (Houston, TX National Association of Corrosion Engineers, 1969). 

Budz, J., Jones, A.G. and Mullin, J.W., 1987b. Agglomeration of potassium sulphate in an MSMPR crystallizer. In Fundamental aspects of crystallization and precipitation processes, American Institute of Chemical Engineers. Symposium Series, No. 253, 83, New York American Institute of Chemical Engineers, pp. 78-84. 

Stephen W. Tsai, Strength Theories of Filamentary Structures, in Fundamental Aspects of Fiber Reinforced Plastic Conposites, Conference Proceedings, R. T. Schwartz and H. S. Schwartz (Editors), Dayton, Ohio, 24-26 May 1966, Wiley interscience. New York, 1966, pp. 3-11. 

The example illustrates how Monte Carlo studies of lattice models can deal with questions which reach far beyond the sheer calculation of phase diagrams. The reason why our particular problem could be studied with such success Hes of course in the fact that it touches a rather fundamental aspect of the physics of amphiphilic systems—the interplay between structure and wetting behavior. In fact, the results should be universal and apply to all systems where structured, disordered phases coexist with non-struc-tured phases. It is this universal character of many issues in surfactant physics which makes these systems so attractive for theoretical physicists. 

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