Cooperative setting for long-range linkage of Ca(2+) binding and ATP synthesis in the Ca(2+) ATPase.

High-affinity and cooperative binding of two Ca(2+) per ATPase (SERCA) occurs within the membrane-bound region of the enzyme. Direct measurements of binding at various Ca(2+) concentrations demonstrate that site-directed mutations within this region interfere selectively with Ca(2+) occupancy of either one or both binding sites and with the cooperative character of the binding isotherms. A transition associated with high affinity and cooperative binding of the second Ca(2+) and the engagement of N796 and E309 are both required to form a phosphoenzyme intermediate with ATP in the forward direction of the cycle and also to form ATP from phosphoenzyme intermediate and ADP in the reverse direction of the cycle. This transition, defined by equilibrium and kinetic characterization of the partial reactions of the enzyme cycle, extends from transmembrane helices to the catalytic site through a long-range linkage and is the mechanistic device for interconversion of binding and phosphorylation potentials

Fast and Accurate Pose Estimation with Unknown Focal Length Using Line Correspondences

Estimating camera pose is one of the key steps in computer vison, photogrammetry and SLAM (Simultaneous Localization and Mapping). It is mainly calculated based on the 2D–3D correspondences of features, including 2D–3D point and line correspondences. If a zoom lens is equipped, the focal length needs to be estimated simultaneously. In this paper, a new method of fast and accurate pose estimation with unknown focal length using two 2D–3D line correspondences and the camera position is proposed. Our core contribution is to convert the PnL (perspective-n-line) problem with 2D–3D line correspondences into an estimation problem with 3D–3D point correspondences. One 3D line and the camera position in the world frame can define a plane, the 2D line projection of the 3D line and the camera position in the camera frame can define another plane, and actually the two planes are the same plane, which is the key geometric characteristic in this paper’s estimation of focal length and pose. We establish the transform between the normal vectors of the two planes with this characteristic, and this transform can be regarded as the camera projection of a 3D point. Then, the pose estimation using 2D–3D line correspondences is converted into pose estimation using 3D–3D point correspondences in intermediate frames, and, lastly, pose estimation can be finished quickly. In addition, using the property whereby the angle between two planes is invariant in both the camera frame and world frame, we can estimate the camera focal length quickly and accurately. Experimental results show that our proposed method has good performance in numerical stability, noise sensitivity and computational speed with synthetic data and real scenarios, and has strong robustness to camera position noise

Fabrication of a 3D Printed Continuous Carbon Fiber Composite Grid Stiffened Structure Using Induction Heating

In aerospace applications, composite grids have been widely utilized to enhance the strength of large thin-shell components. Recently, a growing focus has been on the research of 3D printing continuous fiber-reinforced thermoplastic composites. The 3D printing method offers various advantages over traditional molding processes, including a simpler process, higher material utilization, and lower manufacturing costs. However, the use of 3D printing for manufacturing continuous fiber-reinforced composite structures presents challenges, such as a high occurrence of defects within the structure and insufficient mechanical properties. These limitations hinder its widespread application. To address these issues, this study proposes a method for treating 3D-printed composite grid structures using induction heating. Initially, the induction heating mechanism of 3D-printed composite grids was analyzed by studying the impedance at the junction, including direct contact resistance and dielectric hysteresis loss. Subsequently, the impact of induction heating treatment on internal defects was explored by observing micro morphologies. The results show that the combination of induction heating and vacuum pressure effectively reduces porosities within the 3D-printed carbon fiber composite grids. Additionally, 3D-printed composite grid-stiffened PLA structures were fabricated with induction heating, and the bending and impact tests were conducted to evaluate their mechanical properties. The results indicate that using a grid-unit size of 4 mm leads to significant increases in bending strength and modulus of the grid-stiffened structure, with improvements of 137.6% and 217.8%, respectively, compared to the neat PLA panel. This demonstrates the exceptional mechanical enhancement efficiency of the 3D-printed lightweight composite grids

Four-Dimensionally Printed Continuous Carbon Fiber-Reinforced Shape Memory Polymer Composites with Diverse Deformation Based on an Inhomogeneous Temperature Field

Four-dimensionally printed continuous carbon fiber-reinforced shape memory polymer composite (CFSMPC) is a smart material with the ability to bear loads and undergo deformation. The deformation of CFSMPC can be driven by the electrothermal effect of carbon fibers. In this study, the effect of temperature on the shape memory recovery performance of polylactic acid (PLA) was first studied experimentally. Continuous carbon fibers were incorporated into PLA to design CFSMPCs with thickness gradients and hand-shaped structures, respectively. The distribution strategy of the carbon fibers was determined based on simulations of the electrically driven shape recovery process of the aforementioned structures. Both the simulations and experiments demonstrated that the electrification of the CFSMPC structures resulted in an inhomogeneous temperature field, leading to distinct deformation recovery processes. Eventually, a precise unfolding was achieved for the thickness gradient structure and the five fingers in the hand-shaped structure by utilizing a safe voltage of 6 V. This demonstrates that the 4D-printed CFSMPC with diverse deformations based on an inhomogeneous temperature field has potential applications in actuators, reconfigurable devices, and other fields

Two Possible Side Reaction Pathways during Furanic Etherification

The revealing mechanism of side reactions is crucial for obtaining theoretical yield in industrialization when 2,5-bis(methoxymethyl)furan (BMMF) yield is above 95%. By-products catalyzed by the conventional ZSM-5 (C-ZSM-5) and hierarchical porous ZSM-5 (HP-ZSM-5) catalytic systems were different, and some key by-products were identified. Thus, possible pathways were proposed, which helps to further improve BMMF selectivity. Additionally, HP-ZSM-5 exhibited quicker reaction rate, higher BMMF yield and selectivity, and slower deactivation process. The relatively weak acidity of HP-ZSM-5 suppresses the ring-opening reaction and subsequent side reactions, and introduction of mesopores improves mass transport and slightly increases hydration of 2,5-bis(hydroxymethyl)furan (BHMF)

Two Possible Side Reaction Pathways during Furanic Etherification

The revealing mechanism of side reactions is crucial for obtaining theoretical yield in industrialization when 2,5-bis(methoxymethyl)furan (BMMF) yield is above 95%. By-products catalyzed by the conventional ZSM-5 (C-ZSM-5) and hierarchical porous ZSM-5 (HP-ZSM-5) catalytic systems were different, and some key by-products were identified. Thus, possible pathways were proposed, which helps to further improve BMMF selectivity. Additionally, HP-ZSM-5 exhibited quicker reaction rate, higher BMMF yield and selectivity, and slower deactivation process. The relatively weak acidity of HP-ZSM-5 suppresses the ring-opening reaction and subsequent side reactions, and introduction of mesopores improves mass transport and slightly increases hydration of 2,5-bis(hydroxymethyl)furan (BHMF)

Multi-objective optimization for improving printing efficiency and mechanical properties of 3D-printed continuous plant fibre composites

The mechanical properties and printing efficiency (i.e. the printing time) are often contradictory goals in 3D printing of continuous fibre composites. In this work, we presented a multi-objective optimization method for improving both the mechanical properties and printing efficiency of 3D-printed continuous flax-fibre-reinforced composites (CFFRCs). It was found that the printing efficiency of the CFFRCs with the optimal processing parameters was remarkably improved by 40% without sacrificing the tensile strength of the composites. This study provides an effective method for the improvement of the production efficiency of high-quality 3D-printed continuous fibre reinforced composites

Acidic ZeoliteL as a Highly Efficient Catalyst for Dehydration of Fructose to 5-Hydroxymethylfurfural in Ionic Liquid

ZeoliteL was synthesized by the hydrothermal method and post-treated by NH4 exchange to adjust its acidity. The samples were systematic characterized by various techniques including XRD, X-ray fluorescence spectroscopy, N-2 adsorption-desorption, scanning electron microscopy, pyridine IR spectroscopy, and NH3 temperature-programmed desorption. The results demonstrated that the NH4-exchange post-treatment increased the surface area, micropore volume, and acidity of zeoliteL. The catalytic performance of the samples was tested in the dehydration of fructose to 5-hydroxymethylfurfural (HMF) in ionic liquid (1-butyl-3-methylimidazolium bromide, [bmim]Br). 99.1% yield of HMF was obtained when the KL-80 degrees C-1h sample (KL zeolite treated with 1m NH4NO3 solution at 80 degrees C for 1h) was used. The high efficiency could be attributed to the appropriate acid properties of the catalyst. The zeolite catalyst could be reused four times without significant decrease in activity

Improvement of furanic diether selectivity by adjusting Bronsted and Lewis acidity

Furanic diethers are considered as one of potential biofuels or green solvents. 2,5-Bis(methoxymethyl)furan (BMMF), diether of 2,5-bis(hydroxymethyl)furan (BHMF) with methanol, is difficult to effectively synthesize in traditional homogeneous catalytic systems due to active groups of BHMF. In this case, HCl and AlCl3, representatives of Bronsted and Lewis acid, are separately employed to explore catalytic performance in BHMF etherification. We also demonstrated that Lewis and Bronsted acid not only synergistically catalyze the etherification but also take respectively charge of main and side reactions. Subsequently, the catalytic performance of ZSM-5 and modified ZSM-5 proved this conclusion. High yield and selectivity of BMMF catalyzed by 1.5%Sn-ZSM-5 was obtained, about 95%, which may be attributed to suitable Bronsted and Lewis acidity as well as pore structure. This suggests that synthesis of BMMF by using solid acid is possible in the future industrialization

Towards Generalizable Medical Image Segmentation with Pixel-wise Uncertainty Estimation

Deep neural networks (DNNs) achieve promising performance in visual recognition under the independent and identically distributed (IID) hypothesis. In contrast, the IID hypothesis is not universally guaranteed in numerous real-world applications, especially in medical image analysis. Medical image segmentation is typically formulated as a pixel-wise classification task in which each pixel is classified into a category. However, this formulation ignores the hard-to-classified pixels, e.g., some pixels near the boundary area, as they usually confuse DNNs. In this paper, we first explore that hard-to-classified pixels are associated with high uncertainty. Based on this, we propose a novel framework that utilizes uncertainty estimation to highlight hard-to-classified pixels for DNNs, thereby improving its generalization. We evaluate our method on two popular benchmarks: prostate and fundus datasets. The results of the experiment demonstrate that our method outperforms state-of-the-art methods.Comment: 11 pages, 3 figure