Structural and biochemical basis of FLS2-mediated signal activation and transduction in rice.

The receptor-like kinase FLAGELLIN-SENSITIVE 2 (FLS2) functions as a bacterial flagellin receptor localized on the cell membrane of plants. In Arabidopsis, the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) cooperates with FLS2 to detect the flagellin epitope flg22, resulting in formation of a signaling complex that triggers plant defense responses. However, the co-receptor responsible for recognizing and signaling the flg22 epitope in rice remains to be determined, and the precise structural mechanism underlying FLS2-mediated signal activation and transduction has not been clarified. This study presents the structural characterization of a kinase-dead mutant of the intracellular kinase domain of OsFLS2 (OsFLS2-KDD1013A) in complex with ATP or ADP, resolved at resolutions of 1.98 Å and 2.09 Å, respectively. Structural analysis revealed that OsFLS2 can adopt an active conformation in the absence of phosphorylation, although it exhibits only weak basal catalytic activity for autophosphorylation. Subsequent investigations demonstrated that OsSERK2 effectively phosphorylates OsFLS2, which reciprocally phosphorylates OsSERK2, leading to complete activation of OsSERK2 and rapid phosphorylation of the downstream substrate receptor-like cytoplasmic kinases OsRLCK176 and OsRLCK185. Through mass spectrometry experiments, we successfully identified critical autophosphorylation sites on OsSERK2, as well as sites transphosphorylated by OsFLS2. Furthermore, we demonstrated the interaction between OsSERK2 and OsFLS2, which is enhanced in the presence of flg22. Genetic evidence suggests that OsRLCK176 and OsRLCK185 may function downstream of the OsFLS2-mediated signaling pathway. Our study reveals the molecular mechanism by which OsFLS2 mediates signal transduction pathways in rice and provides a valuable example for understanding RLK-mediated signaling pathways in plants.

Dynamic Characteristics and Effective Stiffness Properties of Sandwich Panels with Hierarchical Hexagonal Honeycomb.

The dynamic characteristics of sandwich panels with a hierarchical hexagonal honeycomb (SP-HHHs) show significant improvements due to their distinct hierarchy configurations. However, this also increases the complexity of structural analysis. To address this issue, the variational asymptotic method was utilized to homogenize the unit cell of the SP-HHH and obtain the equivalent stiffness, establishing a two-dimensional equivalent plate model (2D-EPM). The accuracy and effectiveness of the 2D-EPM were then verified through comparisons with the results from a detailed 3D FE model in terms of the free vibration and frequency- and time-domain forced vibration, as well as through local field recovery analysis at peak and trough times. Furthermore, the tailorability of the typical unit cell was utilized to perform a parametric analysis of the effects of the length and thickness ratios of the first-order hierarchy on the dynamic characteristics of the SP-HHH under periodic loading. The results reveal that the vertices serve as weak points in the SP-HHH, while the vertex cell pattern significantly influences the specific stiffness and stiffness characteristics of the panel. The SP-HHH with hexagonal vertex cells has superior specific stiffness compared to panels with circular and rectangular vertex cells, resulting in a more lightweight design and enhanced stiffness.

Effects of a structural simulation curriculum for the repair of obstetrical anal sphincter injuries.

OBJECTIVE: To assess the short-term and skill-retention effects of a structural simulation curriculum for the repair of obstetrical anal sphincter injuries (OASIS). METHODS: This prepost experimental study recruited 31 obstetrics and gynecology residents from Peking Union Medical College Hospital. OASIS repair skill evaluations (at all timepoints) comprised a task-specific checklist (TSC), global rating scale (GRS), and pass/fail grade. A beef-tongue model was adopted in the simulation curriculum. After baseline testing, residents completed a structured 1-h workshop. Two weeks later, a second test was performed, followed by a one-to-one teaching workshop, with the proper completion of a checklist as the end-point. Three months later, residents completed a third test. RESULTS: The overall pass rate at baseline was 16.1%, with higher GRS scores (p = 0.035) in senior residents. Additionally, previewing the procedure before class and a history of OASIS repair observation were associated with higher TSC and GRS scores. Significant skill improvement was observed in the second and third tests, with pass rates of 96.8% and 93.5% respectively. Both TSC and GRS scores were improved compared with baseline (p < 0.001). CONCLUSION: A structural simulation curriculum integrating deliberate practice under supervision improves OASIS repair competence and achieves satisfactory skill retention.

Investigating the Effective Performance of Sandwich Panel with Petal Star-Triangular Core Using VAM-Based Equivalent Model.

On the basis of star-shaped core sandwich panel, a novel sandwich panel with petal-triangle core (SP-PSC) was proposed to improve the negative Poisson's ratio (NPR) effect while retaining the characteristics of light weight and high strength. To study the complex structure more conveniently and quickly, a variational asymptotic method-based equivalent two-dimensional model (2D-EPM) was developed. The accuracy and efficiency of 2D-EPM were verified by the three-point bending experiment data and the 3D FE model results under different boundary and load conditions. The effects of the geometric parameters on the equivalent stiffness, buckling, natural frequency and NPR effect were also investigated. To increase the NPR of SP-PSC, the material of facesheet was changed from isotropic material to unidirectional CFPR material, and the influence of the material anisotropy on the NPR effect of SP-PSC was investigated. It is found that the NPR of SP-PSC increased first and then decreased with the increase in the fiber angle, reaching the maximum value at 40-50∘. At the same time, this law is applicable to SP-PSC with different material or geometric parameters. Finally, two improved cores, petal star-triangular core with X-shaped ligaments (PSC-X) and double-arc star-shaped core (DSC), were proposed and compared with SP-PSC in equivalent stiffness and recovered local fields to demonstrate their advantages. Compared with the original plate, the stress concentration and equivalent stiffness of the two improved PSCs significantly improved.

A VAM-Based Equivalent Model for Triangular Honeycomb Sandwich Panels: Comparison with Numerical and Experimental Data.

Due to their complex microstructures, the research on the static and dynamic behaviors of triangular honeycomb sandwich panels (triangular HSPs) is limited. In this study, the effective plate properties of triangular HSP was obtained by the homogenizing of the unit cell, and then the input to a VAM-based two-dimensional equivalent plate model (2D-EPM) to perform static and dynamic analyses. The accuracy of the proposed model for predicting the equivalent stiffness of the triangular HSP was verified by three-point bending experiments of 3D-printed specimens. Then, the static displacement, global buckling, and free vibrations predicted by 2D-EPM were verified with the results from three-dimensional finite element model simulations under various boundary conditions. The influences of structural parameters (including angle, core wall thickness, and cell side length of the unit cell) on the static and dynamic characteristics of triangular HSPs were also investigated, which can provide a useful tool for the modeling and evaluation of triangular HSPs under different conditions.

Estimating of the Static and Dynamic Behaviors of Orthogrid-Stiffened FRP Panel Using Reduced-Order Plate Model.

The orthogrid-stiffened FRP panel (OSFP) is a generic structural element in weight-sensitive structure applications. Based on the variational asymptotic method, a 2D reduced-order plate model (2D-RPM) of OSFP was constructed through matching the strain energy of the original panel for static and dynamic analyses. The local field distributions were recovered using the recovery relationship and global response. The relative influences of select parameters on the effective performance of the OSFP were revealed by parametric studies. The comparative results showed that the effective performance of the OSFP predicted by the 2D-RPM were consistent with those predicted by the 3D finite element model, but the computational efficiency was greatly improved. The stiffener height had the greatest influence on the natural frequency of the panel. The layup configurations of laminates had significant influences on the equivalent stiffness and buckling load of the OSFP but had little effect on the vibration modes, which could be varied by adjusting the stiffening forms.

Structural Analysis of Composite Conical Convex-Concave Plate (CCCP) Using VAM-Based Equivalent Model.

Compared with the ordinary foundation plate, the composite conical convex-concave plate (CCCP) has obvious anisotropic characteristics, and there is less research on the relationship between its mechanical properties and structural parameters. In this article, a numerical model for the equivalent stiffness of a typical unit cell with conical convex is established by using the variational asymptotic method. Then, the 3D finite element model (3D-FEM) of CCCP is transformed into 2D equivalent plate model (2D-EPM) with the effective plate properties obtained from the constitutive analysis of unit cell. The accuracy of 2D-EPM is verified by comparing with the displacement, natural frequencies, and buckling results from 3D-FEM under different boundary conditions. Then, the influence of geometric parameters and layup configurations on the effective performances of CCCP are investigated. Finally, the buckling loads and natural frequencies of bidirectional CCCP are compared with those of CCCP by using the present model. The present model is particularly useful in the early design stage of CCCP where many design trade-offs need to be made over a vast design space in terms of material selection, ply angles, and geometric parameters.

Prediction of Bending, Buckling and Free-Vibration Behaviors of 3D Textile Composite Plates by Using VAM-Based Equivalent Model.

To solve the microstructure-related complexity of a three-dimensional textile composite, a novel equivalent model was established based on the variational asymptotic method. The constitutive modeling of 3D unit cell within the plate was performed to obtain the equivalent stiffness, which can be inputted into the 2D equivalent model (2D-EPM) to perform the bending, free-vibration and buckling analysis. The correctness and effectiveness of the 2D-EPM was validated by comparing with the results from 3D FE model (3D-FEM) under various conditions. The influence of yarn width and spacing on the equivalent stiffness was also discussed. Finally, the effective performances of 3D textile composite plate and 2D plain-woven laminate with the same thickness and yarn content were compared. The results revealed that the bending, buckling and free-vibration behaviors predicted by 2D-EPM were in good agreement with 3D-FEM, and the local field distributions within the unit cell of 3D textile composite plate were well captured. Compared with the 2D plain-woven laminate, the displacement of 3D textile composite plate was relatively larger under the uniform load, which may due to the fact that the through-the-thickness constrains of the former are only dependent on the binder yarns, while the warp yarns and weft yarns of the latter are intertwined closely.

Preterm Births in Peking Union Medical College Hospital in the Past 25 Years.

Objective To investigate the changes in preterm birth rate,its gestational age distribution,and possible contributors in Peking Union Medical College Hospital (PUMCH) over the last 25-year period. Methods The clinical data of premature deliveries,both singleton and twins,in PUMCH from January 1,1990 to December 31,2014 were retrospectively analyzed. We counted the number of premature fetuses and assessed the changes of preterm birth rate and its gestational age distribution (including extremely preterm birth,early preterm birth,and late preterm birth) over time. The etiologies (including spontaneous and iatrogenic) of preterm birth were also surveyed. Results The overall preterm birth rate was 7.8% in PUMCH,showing a slightly up-trend in both singletons and twins. Twin prematurity accounted for 23.8% of total preterm births,increased from 15.1% to 28.5%. Preterm births subgrouped by gestational age included 26 cases (0.7%) of extreme prematurity (<28 weeks),1199 cases (33.9%) of early preterm birth (28- 33+6 weeks),and 2310 cases (65.3%) of late preterm birth (34- 36+6 weeks). The gestational age distribution in singletons and twins showed no significant difference(z=0.844,P=0.398). Changes in the proportion of preterm birth before 28 weeks was little,gradually increased in the 28- 33+6 weeks group (from 23.8% to 36.1%) and gradually decreased in the 34- 36+6 weeks group (from 75.5% to 63.3%). Trends of gestational age distribution of singleton and twins were similar to that of the total. Spontaneous preterm labor,preterm premature rupture of membrane,and medically indicated (iatrogenic) preterm birth accounted for 20.2%,38.9%,and 40.9% respectively. There was no difference in singletons and twins(χ2=1.071,P=0.301).The proportion of iatrogenic preterm was increased. Common reasons for iatrogenic preterm birth included gestational hypertension,fetal indications (including fetal distress,fetal growth restriction),placenta previa,and pregnancy complicated by heart disease. Conclusions The overall preterm birth rate shows an upward trend in the general hospital as a result of more multifetal gestations and more medically indicated preterm births. Reducing multifetal gestations and effective control of pregnancy complications should be the priorieties in preterm birth intervention.