A typical feature of proteins from the rhodopsin family is the sensitivity of their absorption band maximum to protein amino acid composition. For this reason, studies of these proteins often require ...methodologies that determine spectral shift caused by amino acid substitutions. Generally, quantum mechanics/molecular mechanics models allow for the calculation of a substitution-induced spectral shift with high accuracy, but their application is not always easy and requires special knowledge. In the present study, we propose simple models that allow us to estimate the direct effect of a charged or polar residue substitution without extensive calculations using only rhodopsin three-dimensional structure and plots or tables that are provided in this article. The models are based on absorption maximum values calculated at the SORCI+Q level of theory for cis- and trans-forms of retinal protonated Schiff base in an external electrostatic field of charges and dipoles. Each value corresponds to a certain position of a charged or polar residue relative to the retinal chromophore. The proposed approach was evaluated against an example set consisting of twelve bovine rhodopsin and sodium pumping rhodopsin mutants. The limits of the applicability of the models are also discussed. The results of our study can be useful for the interpretation of experimental data and for the rational design of rhodopsins with required spectral properties.
Thermo- and soluto-capillarity: Passive and active drops Ryazantsev, Yuri S.; Velarde, Manuel G.; Rubio, Ramón G. ...
Advances in colloid and interface science,
September 2017, 2017-Sep, 2017-09-00, 20170901, Letnik:
247
Journal Article
Recenzirano
A survey is provided of a variety of problems where a passive or an active drop experiences directed motion consequence of the action of an external or internal agent or a combination of both. An ...active drop is capable of reacting by engendering autonomous, self-propelled motion in favor or against the agent. The phenomena involved offer diverse complexity but one way or another the drop motion finally rests on thermo- or soluto-capillarity hence on interfacial tension gradients. Accordingly, here a minimal mathematical framework underlying such drop motions is provided when direct external temperature or solute gradients, illumination, internal heat generation or surface chemical reaction are incorporated into the physico-chemical-hydrodynamics.
Display omitted
•Review of hydrodynamics of passive and active drops/bubbles in host fluids.•Mathematical description of the motion of drops/bubbles due to interfacial tension gradients is itemized.•Force on active and passive drops/bubbles has been provided.•Classical and recent experiments on active and passive motion of drops/bubbles are described.
Display omitted
•Creeping flows of active drops of radii in the millimeter range.•Viscous diffusion transport compatible with fluid itself being of small viscosity.•Low thermal Peclet number flows ...thus disregarding convected heat.•Very high solute Peclet numbers highlighting both diffusion and convected solute.
Thermo-capillary stresses on the surface of a drop can be the result of a non-isothermal surface chemical conversion of a reactant dissolved in the host fluid. The strength of heat production (with e.g. absorption) on the surface is ruled by the diffusion of the reactant and depends on the state of motion of the drop. Such thermo-capillary stresses can provoke the motion of the drop or its motionless state in the presence of an external body force. If in the balance of forces, including indeed viscous drag, the net resultant force vanishes there is the possibility of autonomous motion with constant velocity of the drop. Focusing on drops with radii in the millimeter range provided here is a quantitative study of the possibility of such autonomous motion when the drop, considered as active unit, is seat of endo- or exo-thermic reactive processes that dominate its motion. The framework is restricted to Stokes flows in the hydrodynamics, negligible heat Peclet number while the solute Peclet number is considered very high. A boundary layer approximation is used in the description of reactant diffusion. Those processes eventually end up in the action being expressed by surface tension gradients and the Marangoni effect. Explicit expressions of the force acting on the drop and the velocity fields inside and outside the drop are provided. Some significant particular cases are discussed to illustrate the usefulness of the theory.
Concave spherical feed array for luneberg lens Ryazantsev, Roman O.; Salomatov, Yuri P.; Sugak, Mikhail I.
2013 International Siberian Conference on Control and Communications (SIBCON),
2013-Sept.
Conference Proceeding
This paper presents a design of concave spherical base Vivaldi feed array for beam steering without the use of any phase shifters. The research goal is reached through the use of Luneberg lens ...aperture and switching of active feed array element. Vivaldi array element has solid metal sheet design with stripline feeding for linear polarization. Special elements are used for mutual coupling effects weakening and directional pattern back lobe suppression at low frequencies. The design has such advantages, like broad bandwidth, wide scan angle in azimuth and elevation, low loss level, and machining simplicity of feed array.
PDF
