RESUMO
An unusual expansion dynamics of individual spin crossover nanoparticles is studied by ultrafast transmission electron microscopy. After exposure to nanosecond laser pulses, the particles exhibit considerable length oscillations during and after their expansion. The vibration period of 50-100 ns is of the same order of magnitude as the time that the particles need for a transition from the low-spin to the high-spin state. The observations are explained in Monte Carlo calculations using a model where elastic and thermal coupling between the molecules within a crystalline spin crossover particle govern the phase transition between the two spin states. The experimentally observed length oscillations are in agreement with the calculations, and it is shown that the system undergoes repeated transitions between the two spin states until relaxation in the high-spin state occurs due to energy dissipation. Spin crossover particles are therefore a unique system where a resonant transition between two phases occurs in a phase transformation of first order.
RESUMO
Spin crossover (SCO) is a promising switching phenomenon when implemented in electronic devices as molecules, thin films or nanoparticles. Among the properties modulated along this phenomenon, optically induced mechanical changes are of tremendous importance as they can work as fast light-induced mechanical switches or allow to investigate and control microstructural strains and fatigability. The development of characterization techniques probing nanoscopic behavior with high spatio-temporal resolution allows to trigger and visualize such mechanical changes of individual nanoscopic objects. Here, ultrafast transmission electron microscopy (UTEM) is used to precisely probe the length changes of individual switchable nanoparticles induced thermally by nanosecond laser pulses. This allows revealing of the mechanisms of spin switching, leading to the macroscopic expansion of SCO materials. This study is conducted on individual pure SCO nanoparticles and SCO nanoparticles encapsulating gold nanorods that serve for plasmonic heating under laser pulses. Length changes are compared with time-resolved optical measurements performed on an assembly of these particles.
RESUMO
Objective. The increase of BMI before pregnancy and during pregnancy will lead to hypertensive disorder in pregnancy (HDP) and abnormal glycolipid metabolism, as well as increase the risk of neonatal weight abnormalities and adverse pregnancy outcome. This study retrospectively analyzed the clinical data of 358 women who were admitted to the obstetrics department of our hospital from January 2018 to July 2019. And the relationship between prepregnancy BMI, BMI increase during pregnancy and delivery methods, postpartum hemorrhage, neonatal weight, premature delivery, neonatal asphyxia, gestational diabetes mellitus (GDM), and hypertension during pregnancy (HDP) was observed and compared. The results show that both high BMI before pregnancy and excessive weight gain during pregnancy can lead to the incidence of abnormal birth weight and adverse birth outcome increase. Therefore, in order to reduce the incidence of neonatal weight abnormalities and adverse birth outcomes and to prevent the adverse effects during pregnancy and postpartum, clinically, obese women should be guided to eat according to reasonable diet and exercise to control their weight.
RESUMO
This paper presents a facile approach for the rapid and maskless fabrication of hierarchical structures by multibeam laser interference. In the work, three- and four-beam laser interference lithographies were proposed to fabricate ordered multiscale surface structures instead of six or more beam interference with a complicated system setup. The pitch and shape of hierarchical structures can be controlled by adjusting the parameters of incident light. The experiment results have shown that the hierarchical anisotropy and isotropy surface structures can be fabricated by this method with the control of the parameters of each incident beam, which is in accordance with the theoretical analysis and computer simulations.
