Artificial systems

J- Holland, Adaptation in Natural and Artificial Systems, University of Michigan Press, Michigan, 1975. 

Holland, J.H. (1975) Adaption in natural and artificial systems. The University of Michigan Press, Ann Arbor. 

Stookey s reflection on a lifetime s industrial research is An industrial researcher must bring together the many strings of a complex problem to bring it to a conclusion, to my mind a more difficult and rewarding task than that of the academic researcher who studies one variable of an artificial system . 

Some aspects of the Lowe-Thomeley mechanism for nitrogenase action, which has served us well over the past 15 years, are being called into question. In particular, the necessity for protein-protein dissociation after each electron transfer, the rate-determining step with dithionite as reductant, is being questioned when the natural electron donor flavodoxin or other artificial systems are used. Some aspects of the mechanism should be reinvestigated. 

In the quest for better methods of establishing the environmental safety (or otherwise) of chemicals, interest has grown in the use of microcosms and meso-cosms—artificial systems in which the effects of chemicals on populations and communities can be tested in a controlled way, with replication of treatments. Mesocosms have been defined as bounded and partially enclosed outdoor units that closely resemble the natural environment, especially the aquatic environment (Crossland 1994). Microcosms are smaller and less complex multispecies systems. They are less comparable with the real world than are mesocosms. Experimental ponds and model streams are examples of mesocosms (for examples, see Caquet et al. 2000, Giddings et al. 2001, and Solomon et al. 2001). The effects of chemicals at the levels of population and community can be tested in mesocosms, although the extent to which such effects can be related to events in the natural environment is questionable. Although mesocosms have been developed by both industrial... 

In order to distinguish these orbitals from their Hartree-Fock counterparts, they are usually termed Kohn-Sham orbitals, or briefly KS orbitals. The connection of this artificial system to the one we are really interested in is now established by choosing the effective potential Vs such that the density resulting from the summation of the moduli of the squared orbitals tpj exactly equals the ground state density of our real target system of interacting electrons,... 

No less important are studies of the aggregation-induced effects in artificial systems with the objective of harvesting solar radiation. One of the potential applications of carotenoids is their use... 

Polivka, T. and V. Sundstrom. 2004. Ultrafast dynamics of carotenoid excited states—From solution to natural and artificial systems. Chem. Rev. 104 2021-2071. 

Carotenoids are highly lipophilic an active area of research concerns how carotenoids interact with and affect membrane systems (see Chapters 2 and 10). Also, the lipid solubility of these compounds has important implications for carotenoid intestinal absorption (see Chapter 17) models such as the Caco-2 cell model are being used to conduct detailed studies of carotenoid absorption/ competition for absorption (Chapter 18). The lipid solubility of these carotenoids also leads to the aggregation of carotenoids (see Chapter 3). Carotenoids aggregate both in natural and artificial systems, with implications for carotenoid excited states (see Chapter 8). This has implications for a new indication for carotenoids, namely, serving as potential materials for harnessing solar energy. 

Photochemical fixation of carbon dioxide is a function of green plants and some bacteria in nature in the form of photosynthesis. All living organisms on the Earth are indebted directly or indirectly to photosynthesis. Thus, many attempts have been made to simulate the photosynthetic system and make artificial systems, although to date very little success has been achieved. 

Much has been written about artifical solar-energy converters - the reader is referred to references 10, 12, 14-17 for detailed treatments. Here I shall deal exclusively with those artificial systems designed to mimic various aspects of the photosynthesis reaction. 

Kr Fission of 238U for natural systems. Fission of 235U and 239Pu for artificial systems. Only anthropogenic 85Kr is quantitatively important. 1 to 40 years... 

Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. This process is involved in many organic photochemical reactions. It plays a major role in photosynthesis and in artificial systems for the conversion of solar energy based on photoinduced charge separation. Fluorescence quenching experiments provide a useful insight into the electron transfer processes occurring in these systems. 

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