Physical Perturbation Research Articles

Solvent Effects on Electronic Spectra

Abstract Electronic absorption and emission spectra of a molecule dissolved in a solvent medium in general are shifted in energy relative to the spectra of the isolated molecule. In some cases, these solvent shifts amount to more than 30% of the energy of the isolated-molecule transition, although shifts of the order of 102 to 103 cm-1 are more common. These effects have been the subjects of many investigations directed toward defining the molecular bases of the shifts [1–14]. Two broad categories of shift phenomena have been defined: (1) Many, especially the larger, shifts are attributed to specific chemical effects of the solvent on one or both electronic states of the chromaphore. Some important specific effects are: hydrogen-bond formation; proton or charge transfer between solvent and solute; and solvent-dependent aggregation, ionization, and isomerization equilibria. Such specific effects are outside the scope of this discussion. (2) The second broad category of shifts are attributed to physical interactions between the solute and solvent molecules. These interactions must be considered even when the chromaphore is not involved in a solvent-dependent reaction. Theories of these general effects assume that the chemical states of the isolated (at low pressure in the vapor phase) and solvated chromaphore are the same as a zeroth-order approximation and treat the solvent effects as a physical perturbation of the relevant molecular states of the chromaphore. Frequently, only perturbations due to attractive intermolecular interactions are included in the analysis.

Life histories and the role of disturbance

An alternative to the stability-time hypothesis explaining the high benthic faunal diversities in the deep sea ( Sanders, 1968; Slobodkin and Sanders, 1969) has been proposed by Dayton and Hessler (1972). According to Dayton and Hessler, nonselective predation reduces competition between species thereby allowing more species to coexist. Much controversy relating to the concept of diversity and what it implies can be resolved by realizing that an increase of within-habitat diversity is achieved by two entirely different and unrelated pathways. The resultant diversities are differentiated as follows: short-term, non-equilibrium, or transient diversity—induced by a low level or unpredictable physical or biological perturbation or stress resulting in biological ‘undersaturation’. Long-term or evolutionary diversity—increase in diversity is the product of past biological interactions in physical benign and predictable environments. Although predation may play a role in the evolution of deep-sea species, the life histories indicate that it does not seem a likely means for control of population size, regardless of whether predation is selective or non-selective. The known life history characteristics of deep-sea animals—small brood size, age-class structure not dominated by younger stages, probable slow growth rates—are features that neither would be expected nor have high survival value in predator-controlled communities or any environment where short-term or transient diversity is important. Non-selective cropping proposed by Dayton and Hessler as a mechanism for controlling population size of prey species would result in rapid extinction of species with relatively low reproductive rates. In addition to feeding behavior, niche diversification may be the product of biochemical specialization, biotic relationships and microhabitat specialization. Niche diversification may also result from adaptation to different parts of a temporal mosaic. The stability-time hypothesis does not state that disturbance plays no role in predictable environments. The relative predictability of the environment enables species to survive with lower reproductive rates, lower mortality rates, and smaller population size. Rates of competitive exclusion are lower and species are able to become more specialized on both biotic and physical components of the environment. Control of population size is seldom the result of changes in the physical environment or any disturbance, including predation, so that we may say that the community is biologically accommodated rather than physically regulated.

The spin hamiltonian

The author derives a spin hamiltonian V(S) for the g fold degenerate level of a system perturbed in first order by a physical perturbation V; the derivation explicitly relates the coefficients a, b, c,... of V(S) to the matrix elements VMM' of V between the zero order physical basis functions psi M. He shows how the symmetry of V and time reversal affect V(S), and considers three often treated examples as an illustration of the power and unity of his method.

The origin of manganese nodules on the ocean floor : Bonatti Enrico and Y. Rammohanroy Nayudu 1965. Am. J. Sci., 263 (1): 17–39

Habitat restoration and recolonisation of benthic communities after physical perturbation in the deep sea has long been thought to be extremely slow. This study reports on a serendipitous opportunity to survey the current state of a large mechanical disturbance of sediments at 6460 m in the Pacific Ocean. The impact was caused 77 years ago by the sinking of the USS Johnston. The surrounding debris field had little impact on the sedimentary habitat, other than in the provision of artificial hard substrates, while the troughs that formed as the ship impacted the seafloor and slid down the slope of the Philippine Trench were still completely void of animal tracks and burrows, or any observable epifauna, and in some areas subsurface stratification was still exposed at the surface. This suggests that mechanical perturbations of sediments in the deep Pacific may remain ecologically significant for, at the very least, 100 years.

Noise in driven systems

It is known that a direct relation exists between the noise in a system in equilibrium and transient drift toward equilibrium. It seems that a similar relation should exist for a system in a nonequilibrium stationary state. It is now necessary to distinguish between two types of transients; those produced by selecting those systems satisfying certain initial and those produced by actual physical perturbation. It is shown that a simple relation exists between noise and the transients produced by selection and that no relation exists in the case of transients produced by perturbation. In the equilibrium case it is shown that the two types of transients, though still logically and operationally distinct, can be described by the same impedance operator.