悬臂梁中开闭裂纹的损伤识别

利用裂纹诱导弦挠度函数,建立了悬臂Euler-Bernoulli中开闭裂纹位置、深度、初始张开角等损伤参数的识别方法.为此,首先将梁中开闭裂纹等效为单向扭转弹簧,给出了考虑裂纹缝隙效应的裂纹梁等效抗弯刚度,并得到悬臂Euler-Bernoulli开闭裂纹梁弯曲挠度的显式闭合解及裂纹诱导弦挠度函数,证明了裂纹诱导弦挠度的...     

A Potential Alternative to Polystyrene: Ring-opening Terpolymerization of Different Epoxides with Phthalic Anhydride Using Metal-free Dual Catalysts

A series of semi-aromatic polyesters named as Poly(PO-CHO-PA) were facilely synthesized via ring-opening terpolymerization of biobased cyclohexane oxide(CHO)/propylene oxide(PO)/phthalic anhydride(PA) using economical U1/PPNCl as dual catalyst. The proportion of CHO-PA and PO-PA segments in polymer can be readily altered by changing the feed ratio of CHO/PO because the reactivity ratios of CHO and PO with PA calculated by Fineman-Ross method are comparable. All synthesized amorphous polyesters with various compositions show one Tg ranging from 62 ℃ to 133 ℃. Significantly, the mechanical, thermal and barrier properties of these amorphous semi-aromatic polyesters are also adjustable and investigated for the first time. The results indicate the semi-polyesters exhibit superior thermostability(T5% ranging from 306 ℃ to323 ℃) and high tensile strength(40.21-55.7 MPa) that is comparable with polystyrene(PS). Furthermore, Poly(PO-CHO-PA) films possess a promising prospect as packaging materials because of its colorless and highly transparent nature, along with low oxygen and water vapor transmission rate. All above performances may guarantee its potential alternative to commercial PS.     

Flowfield of a helicopter submerged inlet with power output shaft

The submerged inlet is an attractive configuration for advanced helicopters due to its high stealth performance and low external drag.In this paper,a submerged ...     

一种可能的简并谱NNS分布

To expose the statistical properties of the degenerated spectrum, with the aid of the random matrix theory,a possible form of the NNS distribution function of the degenerate spectrum was proposed by providing a solution in terms of the same-degeneracy case. The results indicate that the target spectrum is transformed into two sub-spectra: a random one and a regular one, and that the repulsion level of the regular spectrum is also decreased.     

Synthesis and Crystal Structure of 3,（5-Amino-4-ethoxycarbonyl-3-methylthio-1-H- pyrazolyl）-5-phenyl-1,2,4-triazine

1 INTRODUCTION Substituted 1,2,4-triazines represent an important class of nitrogen-containing heterocycles. The 1,2, 4-triazine core is a versatile synthetic platform to access a wide range of condensed heterocyclic ring systems via intramolecular Diels-Alder reactions with a vast array of dienophiles[1~5]. In addition, 1,2, 4-triazines have been associated with diverse activi- ties such as antihypertension and inhibition of pla- telets[6] and antiinflammatory[7], and been a key com- po…     

非化学配比锰基钙钛矿输运特性研究

本文报道了用溶胶凝胶法并经过低温(900℃)后处理制备的具有非化学配比的La2/3Ca1/3Mn1-xO3(x=0～0.10)多晶样品的电输运和磁性质的实验研究.结果表明,随x的增加,样品呈现出明显增强的非本征磁电阻效应,同时其本征磁电阻效应减弱.实验还观察到样品的颗粒尺寸随x的增加而减小的现象.基于样品的结构特征,本文讨论了其独特输运性能的形成原因.     

碱金属及碱土金属离子化合物溶解性变化规律

对碱金属、碱土金属离子化合物的溶解性与正负离子半径差Δr的变化关系进行了探讨,总结出碱金属、碱土金属同族化合物溶解性随Δr的变化有以下3种情况:(1)随Δr增大,溶解度s随之增大;(2)随Δr增大,s反而减小;(3)随Δr增大,s变化不规则。在此基础上,通过碱金属、碱土金属同族化合物晶格能U、离子水合焓ΔHh、溶解过程的焓变ΔHs和自由能变ΔGs等热力学量的递变对其溶解性随Δr的变化作出了解释。     

2′-O-Methyl modified guide RNA promotes the single nucleotide polymorphism (SNP) discrimination ability of CRISPR–Cas12a systems

The CRISPR–Cas12a system has been widely applied to genome editing and molecular diagnostics. However, off-target cleavages and false-positive results remain as major concerns in Cas12a practical applications. Herein, we propose a strategy by utilizing the 2′-O-methyl (2′-OMe) modified guide RNA (gRNA) to promote the Cas12a''s specificity. Gibbs free energy analysis demonstrates that the 2′-OMe modifications at the 3′-end of gRNA effectively suppress the Cas12a''s overall non-specific affinity while maintaining high on-target affinity. For general application illustrations, HBV genotyping and SARS-CoV-2 D614G mutant biosensing platforms are developed to validate the enhanced Cas12a''s specificity. Our results indicate that the 2′-OMe modified gRNAs could discriminate single-base mutations with at least two-fold enhanced specificity compared to unmodified gRNAs. Furthermore, we investigate the enhancing mechanisms of the 2′-OMe modified Cas12a systems by molecular docking simulations and the results suggest that the 2′-OMe modifications at the 3′-end of gRNA reduce the Cas12a''s binding activity to off-target DNA. This work offers a versatile and universal gRNA design strategy for highly specific Cas12a system development.

This study illustrates that 2′-O-methyl modified gRNAs improve the specificity of the CRISPR–Cas12a system (mg-CRISPR) via suppressing the Cas12a''s affinity to off-target DNA and provides an efficient strategy for high-specificity gRNA design.     

Discovery of Novel Pleuromutilin Derivatives as Potent Antibacterial Agents for the Treatment of MRSA Infection

A series of novel pleuromutilin derivatives containing nitrogen groups on the side chain of C14 were synthesized under mild conditions. Most of the synthesized derivatives displayed potent antibacterial activities. Compound 9 was found to be the most active antibacterial derivative against MRSA (MIC = 0.06 μg/mL). Furthermore, the result of time-kill curves showed that compound 9 had a certain inhibitory effect against MRSA in vitro. Moreover, according to a surface plasmon resonance (SPR) study, compound 9 (K_D = 1.77 × 10⁻⁸ M) showed stronger affinity to the 50S ribosome than tiamulin (K_D = 2.50 × 10⁻⁸ M). The antibacterial activity of compound 9 was further evaluated in an MRSA-infected murine thigh model. Compared to the negative control group, tiamulin reduced MRSA load (~0.7 log₁₀ CFU/mL), and compound 9 performed a treatment effect (~1.3 log₁₀ CFU/mL). In addition, compound 9 was evaluated in CYP450 inhibition assay and showed only moderate in vitro CYP3A4 inhibition (IC₅₀ = 2.92 μg/mL).