In these cases, the way the expression of the auto-regulator responds to changes in the concentrations of the “”input” regulators (the response function) is obviously affected by the auto-regulation. We suggest that, conversely, auto-regulation may be used to optimize this response function. To test this hypothesis, we use an evolutionary algorithm and a chemical-physical model of transcription regulation to design model cis-regulatory constructs with MI-503 supplier predefined response functions. In these simulations, auto-regulation
can evolve if this provides a functional benefit. When selecting for a series of elementary response functions-Boolean logic gates and linear responses-the cis-regulatory regions resulting from the simulations indeed often exploit auto-regulation. Surprisingly, the resulting constructs use auto-activation rather than
auto-repression. Several design principles show up repeatedly in the simulation results. They demonstrate how auto-activation can be used to generate sharp, switch-like activation and repression circuits and how linearly decreasing response functions can be obtained. Auto-repression, on the other hand, resulted only when a high response speed or a suppression of intrinsic noise was also selected for. The results suggest that, PD-L1 inhibitor while auto-repression may primarily be valuable to improve the dynamical properties of regulatory circuits, auto-activation is likely to evolve even when selection acts on the shape of response function only.”
“The variation of luminescence and excitation spectra of titanium doped Al2O3 for the concentration of Ti ranging from 10 to 1000 ppm was investigated using synchrotron radiation. In the lightly doped Al2O3-Ti (< 100 ppm) samples we identified several emission bands. These are the emission of the excitons localized at Ti (290 nm), the emission due to F+ centers
(325 nm), the band around 420 nm traditionally attributed to F center emission, and the luminescence of Ti3+ ions at 720 nm. The emphasis in this study is on the clarification of the nature of the blue emission band in the samples with high concentration of Ti (>= 100 ppm), where the luminescence and excitation spectra of the blue emission exhibit selleck screening library noticeable variability. This is explained by a model of the luminescence process of Ti4+-F centers that includes the photoionization of Ti3+, the subsequent capture of electrons at F+-centers, formation of excited F-centers and, finally, the emission of a blue photon. The quenching of the blue emission with increasing Ti concentration is interpreted in terms of competition between oxygen vacancies and Ti4+ centers in the capture of the electron. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552943]“
“Background: Hypertension may be a either a cause or an effect of kidney disease.