Global perturbation

Khan AA, Betel D, Miller ML et al (2009) Transfection of small RNAs globally perturbs gene regulation by endogenous microRNAs. Nat Biotechnol 27 549-555... 

Thus far we have considered only the quantities f(r) and s(r) as indices of chemical reactivity. These quantities, however, are local responses to the global perturbations dJf and dfi, respectively. Chemical reactions proreed by nonlocal responses of one reactant to nonlocal perturbations generated in chemical attack by another reactant. Thus, a fifth issue emerges, how to define nonlocal reactivity indices. Berkowitz and Parr (BP) [15] addressed this issue by introducing the softness kernel,... 

Thirty years of research with bacteriorhodopsin has provided answers to many questions about how protons are transported by transmembrane pumps. In this small seven-transmembrane protein, absorption of light by the retinal chromophore Initiates a reaction cycle in which the initial state recovers through multiple conformational changes of the retinal and the protein, and a proton Is translocated stepwise from one side of the membrane to the other. Spectroscopy, extensive use of site-specific mutations, and crystallography have defined the photocycle reactions in atomic detail and provide a step-by-step description of the proton transfers, the transient local and global perturbations in the protein and how they arise, and the energy flow through the system, which add up to the mechanism of the pump. 

In Table 6.4, the variation of the 3p i — 2po spacing, which follows the same trend as the 2p — 2po spacing for Li and (Li,0) with respect to the EM value, indicates a global perturbation of the electronic potential in the vicinity of the centre, and the changes in the values of these spacings are assumed to also provide a qualitative estimation of the perturbation for more complex centres. 

Of the elements listed in Table 2-3 global perturbations are most dramatically seen for lead. Present-day levels of lead in Americans and Europeans are probably two to three orders of magnitude higher than those of pretechnological humans, as evidenced from studies on blood... 

In spite of the measures taken to reduce anthropogenic emissions of chemical compounds, the impact of regional and global perturbations on atmospheric composition remains large and is expected to intensify in the next decades. Economic development, expansion of urbanization, and the accompanying rise in the emissions of greenhouse gases and of ozone precursors in Asia and South America are expected to be rapid over the next decades. 

Dall Acqua et al., 1998 Sundberg et al, 2000). Such changes, though localized, may result in global perturbations in electrostatic fields or vibrational modes within the interface. 

When an optimum is reached, the perturbation ia any direction would reduce the value of the objective function. Such an optimum, however, does not guarantee a global optimum, and the mountain-climbing process stops at a local optimum. 

A TBma,) explicit functions of the available concentrations of the other nutrients. This approach allows for a pronounced interdependence between the fluxes of the different nutrients but it does not ensure that the Redfield ratios are maintained. In the second approach the contents of the nutrients in the biota reservoir are forced to remain close to the Redfield ratios. This method was used by Mackenzie et al. (1993) in their study of the global cycles of C, N, P, and S and their interactions. They were able to demonstrate how a human perturbation in one of these element cycles could influence the cycles of the other elements. 

Five components of the hydrosphere play major roles in climate feedbacks - atmospheric moisture, clouds, snow and ice, land surface, and oceans. Changes to the hydrologic cycle, among other things, as a result of altered climate conditions are then referred to as responses. Interactions with climate can best be explored by examirung potential response to a climate perturbation, in this case, predicted global warming. 

Lerman et al. (1975) considered several cases in which mankind s activities perturbed the natural cycle. If we assume that all mined P is supplied to the land as fertilizer and that all of this P is incorporated into land biota, the mass of the land biota will increase by 20%. This amount is small relative to the P stored in the land reservoir. Since P incorporated into land biota must first decompose and be returned to the land reservoir before being transported further, there is essentially no change in the other reservoirs. Thus, although such inputs would significantly alter the freshwater-terrestrial ecosystem locally where the P release is concentrated, the global cycle would be essentially unaffected. 

In most of the world s watercourses, dramatic modifications have occurred as a consequence of their intensive use by human societies [1]. Pollution, water abstraction, riparian simplification, bank alteration, straightening of watercourses, dam construction, and species introduction are widespread perturbations in river ecosystems. These human-driven alterations are part of global changes. The simplification of the channel network and the alteration of water fluxes reduce the capacity of fluvial systems to recover from namral disturbances. Hydrologic alterations affect the functional organisation of streams and rivers, and lead to a simplification and impoverishment of the biota within these ecosystems. 

These treatments of periodic parts of the dipole moment operator are supported by several studies which show that, for large oligomeric chains, the perturbed electronic density exhibits a periodic potential in the middle of the chain whereas the chain end effects are related to the charge transfer through the chain [20-21]. Obviously, approaches based on truncated dipole moment operators still need to demonstrate that the global polarization effects are accounted for. In other words, one has to ensure that the polymeric value corresponds to the asymptotic limit of the oligomeric results obtained with the full operator. 

Modulation of DNA structure and dynamics is also possible using base-pair mismatches. Mismatches exert little influence on the global structure of B-DNA duplexes. Locally, the extent of base stacking perturbation depends sensitively on the nature of the mismatch [139-141]. Therefore, while a CA mismatch introduces a significant distortion in local stacking, the well-stacked GA mismatch is, by many criteria, barely perceptible. The dynamics of mismatched base-pairs may also be significantly distinct from matched Watson-Crick base pairs [9]. We exploit these features of DNA mismatches to probe the sensitivity of DNA-mediated CT to base structure and dynamics. 

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