Ultrafast structural changes direct the first molecular events of vision

視覚に関わるタンパク質の超高速分子動画 --薄暗いところで光を感じる仕組み--. 京都大学プレスリリース. 2023-03-23.Vision is initiated by the rhodopsin family of light-sensitive G protein-coupled receptors (GPCRs). A photon is absorbed by the 11-cis retinal chromophore of rhodopsin, which isomerizes within 200 femtoseconds to the all-trans conformation, thereby initiating the cellular signal transduction processes that ultimately lead to vision. However, the intramolecular mechanism by which the photoactivated retinal induces the activation events inside rhodopsin remains experimentally unclear. Here we use ultrafast time-resolved crystallography at room temperature to determine how an isomerized twisted all-trans retinal stores the photon energy that is required to initiate the protein conformational changes associated with the formation of the G protein-binding signalling state. The distorted retinal at a 1-ps time delay after photoactivation has pulled away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space. Notably, the very early structural motions in the protein side chains of rhodopsin appear in regions that are involved in later stages of the conserved class A GPCR activation mechanism. Our study sheds light on the earliest stages of vision in vertebrates and points to fundamental aspects of the molecular mechanisms of agonist-mediated GPCR activation

An analytical algorithm to determine allowable ampacities of horizontally installed rectangular bus bars

The main objective of this paper is to propose an algorithm for the determination of the allowable ampacities of single rectangular-section bus bars without the occurrence of correction factors. Without correction factors, the ampacity computation of the copper and aluminium bus bars is fully automatized. The analytical algorithm has been implemented in a computer program code that along with the allowable ampacity can compute the bus bar temperature and the individual heat transfer coefficient for each side of the bus bar, as well as their corresponding power losses. Natural and forced convection correlations for rectangular bus bars are applied. Effects of the solar radiation and radiation heat losses from the bus bar surface are taken into consideration as well. The finite element method (FEM) has been used for the linear/non-linear steady-state thermal analysis, i.e. for validation of the analytical algorithm. All FEM-based numerical computations were carried out using the COMSOL Heat Transfer Module. [Projekat Ministarstva nauke Republike Srbije, br. TR33046

Optimizing of the cable bedding and the ampacity of underground power cables in trefoil formation by using the gravitational search algorithm

This paper considers the problem of the determination of the optimum values for dimensions of cable trench and cable bedding, interaxial spacings between power cables in trefoil formation and cable ampacities. This non-linear multi-objective optimization problem with constraints is solved by using the gravitational search algorithm (GSA). The procedure used in this paper has allowed the simultaneous inclusion of all control variables into the optimization process and the determination of an optimal solution in accordance with specified optimization criteria. in the present case, the optimal solution is obtained based on the following optimization criteria: (i) minimization of the total installation cost for cable line, (ii) maximization of the cable ampacity and (iii) a simultaneous application of the minimization of the total installation cost for cable line and the maximization of the cable ampacity. The constraints on control variables are introduced through penalty factors which expand the objective function, it is also assumed that the cable ampacity corresponds to a load factor of 0.8. The procedure is carried out with respect to the drying out effect in the soil surrounding the cables

Controlling the thermal environment of underground power cables adjacent to heating pipeline using the pavement surface radiation properties

This paper shows how the pavement surface radiation properties can be used to control the thermal environment of 110 kV underground cables in order to increase their ampacity. It is assumed that the ampacity is additionally affected by the cable bedding size and an underground heating pipeline. Thanks to an experimental apparatus, some useful data were collected for the validation of two different finite element method based models that predict the effect of the pavement surface radiation properties on the cable ampacity. The first model corresponds to the experimental apparatus and actual indoor conditions, while the second one corresponds to the theoretical case and assumed outdoor conditions (taking into account the thermal effects of solar radiation, cable bedding size, and heating pipeline). This paper examines two possible cases of outdoor conditions, one corresponding to summer period (the most unfavorable ambient conditions) and another one corresponding to winter period (the most common winter conditions in Serbia). This proposed new method is based on the experimental data and generalized using the finite element method in COMSOL. It is found that the ampacity of the considered 110 kV cable line can be increased up to 25.4 % for the most unfavorable ambient conditions and up to 8 % for the most common winter conditions. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR33046

High electrical conductivity and high porosity in a Guest@MOF material : Evidence of TCNQ ordering within Cu₃BTC₂ micropores

The host-guest system TCNQ@Cu3BTC2 (TCNQ = 7,7,8,8-tetracyanoquinodimethane, BTC = 1,3,5-benzenetricarboxylate) is a striking example of how semiconductivity can be introduced by guest incorporation in an otherwise insulating parent material. Exhibiting both microporosity and semiconducting behavior such materials offer exciting opportunities as next-generation sensor materials. Here, we apply a solvent-free vapor phase loading under rigorous exclusion of moisture, obtaining a series of the general formula xTCNQ@Cu3BTC2 (0 ≤ x ≤ 1.0). By using powder X-ray diffraction, infrared and X-ray absorption spectroscopy together with scanning electron microscopy and porosimetry, we provide the first structural evidence for a systematic preferential arrangement of TCNQ along the (111) lattice plane and the bridging coordination motif to two neighbouring Cu-paddlewheels, as was predicted by theory. For 1.0TCNQ@Cu3BTC2 we find a specific electrical conductivity of up to 1.5 × 10-4 S cm-1 whilst maintaining a high BET surface area of 573.7 m2 g-1. These values are unmatched by MOFs with equally high electrical conductivity, making the material attractive for applications such as super capacitors and chemiresistors. Our results represent the crucial missing link needed to firmly establish the structure-property relationship revealed in TCNQ@Cu3BTC2, thereby creating a sound basis for using this as a design principle for electrically conducting MOFs.</p