Size-dependent thermomechanical vibration characteristics of rotating pre-twisted functionally graded shear deformable microbeams

A three-dimensional(3D)thermomechanical vibration model is developed for rotating pre-twisted functionally graded(FG)microbeams according to the refined shear deformation theory(RSDT)and the modified couple stress theory(MCST).The material properties are assumed to follow a power-law distribution along the chordwise direction.The model introduces one axial stretching variable and four transverse deflection variables including two pure bending components and two pure shear ones.The complex modal analysis and assumed mode methods are used to solve the governing equations of motion under different boundary conditions(BCs).Several examples are presented to verify the effectiveness of the developed model.By coupling the slenderness ratio,gradient index,rotation speed,and size effect with the pre-twisted angle,the effects of these factors on the thermomechanical vibration of the microbeam with different BCs are investigated.It is found that with the increase in the pre-twisted angle,the critical slenderness ratio and gradient index corresponding to the thermal instability of the microbeam increase,while the critical material length scale parameter(MLSP)and rotation speed decrease.The sensitivity of the fundamental frequency to temperature increases with the increasing slenderness ratio and gradient index,and decreases with the other increasing parameters.Moreover,the size effect can suppress the dynamic stiffening effect and enhance the Coriolis effect.Finally,the mode transition is quantitatively demonstrated by a modal assurance criterion(MAC).

Anaerobic environment as an efficient approach to improve the photostability of fatty acid photodecarboxylase

Fatty acid photodecarboxylase of Chlorella variabilis NC64A(CvFAP) is a novel photoenzyme with great potential in the treatment of waste lipids and production of sustainable aviation fuel. However, the fragile nature of Cv FAP to blue light is an urgent challenge. Herein, we demonstrated anaerobic environment could significantly improve the photostability of Cv FAP for the first time. The decarboxylation of palmitic acid by Cv FAP for 3 h under anaerobic environment increased pentadecane yield by 44.7% as compared to that under aerobic environment. The residual activity of Cv FAP after blue-light preillumination in the absence of palmitic acid for 0.5 h under anaerobic environment was 80.4%, which was 258.7 times higher than that under aerobic environment. Remarkable accumulation of superoxide radical and singlet oxygen in Cv FAP under aerobic environment led to the poor photostability of Cv FAP. Anaerobic environment helped to mitigate the production of superoxide radical and singlet oxygen in Cv FAP, improving the photostability of Cv FAP.

Carboxylic acid reductases enable intramolecular lactamization reactions

As a versatile type of enzyme,carboxylic acid reductases(CAR)can not only reduce various carboxylic acids to aldehydes in cooperation with cofactors ATP and NADPH but also catalyze the synthesis of amides and esters in the absence of NADPH.Here,we report an intramolecular cyclization catalyzed by CAR only with the use of ATP to transform amino acids into diverse lactams,includingγ-/δ-/ε-lactams and chiral derivatives thereof.The observed wide substrate scope and selectivity enable potential applications to be implemented.Our results demonstrate that CAR-catalyzed lactamization is a promising approach for the synthesis of chiral lactam com-pounds under mild conditions,thereby enriching the toolbox for the biosynthesis of lactams as a viable alternative to purely chemical procedures.