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This paper presents a unified Lyapunov-based predefined-time stability theorem that includes three sufficient conditions. The standard theoretical analysis method for achieving predefined-time stability of non-linear systems using this theorem is provided within the framework of Lyapunov theory. The developed Lyapunov-based theorem facilitates the establishment of equivalence between the existing Lyapunov theorems concerning predefined-time stability. Furthermore, when the presented sufficient conditions are relaxed, the predefined-time stability conclusion for non-linear systems degenerates into a finite-time one. Consequently, a standard non-singular sliding mode control framework based on the unified Lyapunov-based theorem is developed for a Lagrangian system to ensure its predefined-time stability. Exemplary numerical simulation results are subsequently given, in order to illustrate the convergence behavior of the system states and confirm that the controlled systems are predefined-time stable. [ABSTRACT FROM AUTHOR]

This paper investigates the appointed‐time attitude stabilization problem of a rigid spacecraft under disturbance and parametric uncertainty. A continuous appointed‐time sliding mode disturbance observer is presented to observe the synthetical disturbance term. To circumvent the singularity problem in terminal sliding mode control, a new nonsingular appointed‐time sliding mode surface is designed by employing the concept of switching control. Based on the observation information deriving from the proposed disturbance observer, an observer‐based nonsingular sliding mode control scheme is developed to stabilize the attitude control system within appointed time which is given by the user. And also, the undesired control chattering phenomenon can be attenuated. The appointed‐time stability of the controlled attitude system is proved by the Lyapunov criteria. The simulation results show that the proposed attitude stabilization control scheme is valid. [ABSTRACT FROM AUTHOR]

The prescribed convergence time control issue of spacecraft with parametric uncertainty in inertia and disturbance is investigated. An adaptive sliding mode control solution is given. As a stepping stone, a new practical predefined-time stability theorem is established for a class of nonlinear systems. Its maximum convergence time is independent of initial states and explicitly prescribed via a gain given by the users. An adaptive predefined-time sliding-mode manifold is then developed. A chattering-free and nonsingular predefined-time controller is finally designed. The spacecraft attitude dynamics' states are governed into a tiny neighborhood with arbitrary small radius after the prescribed time. The performance of this control solution is validated through two simulation examples. [ABSTRACT FROM AUTHOR]

Along with the living environment, organisms have evolved structures that adapt to specific environments and have better mechanical properties. Bioinspired materials learn from nature and improve their mechanical properties by imitating the structure of living organisms. Based on the 4D printed shape memory polymer and the bioinspired design method, this research proposes a soft and hard phase hybrid bioinspired metamaterial with shape memory effect and programmable mechanical properties. Compared with traditional nacre-like materials, bioinspired materials have adjustable characteristics of mechanical properties, impact resistance, and low-frequency vibration isolation. First, based on the constitutive relation of SMP (Shape memory polymer) material and its numerical simulation, an intelligent bioinspired metamaterial is designed. Subsequently, the mechanical properties and vibration isolation behavior and adjustability performance of multi-scale bioinspired metamaterials are explained by experiments. Finally, the adjustable functional mechanism of the deformation and vibration isolation of the bioinspired metamaterial is described. The research of these bioinspired metamaterials has broad application prospects in the fields of impact protection and low-frequency vibration absorption. [ABSTRACT FROM AUTHOR]

The attitude tracking control problem of rigid spacecraft subjected to external disturbance and prescribed performance is studied. A fast fixed‐time stability theorem is firstly developed. A continuous disturbance observer is then designed with its estimation error can be driven into a tiny neighborhood containing zero within fixed time. Moreover, the spacecraft attitude tracking error constrained by prescribed performance function is transformed into an unconstrained dynamics. A disturbance observer‐based prescribed performance tracking controller is designed to stabilize the unconstrained dynamics within fixed time. It also means that the attitude tracking errors meet the prescribed performance as the stabilization of the unconstrained dynamics. Spacecraft simulation examples are finally given to validate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

The dynamic prediction of large spacecraft is a time-consuming process. The impulse-based substructuring (IBS) method is an efficient and accurate method for the dynamic analysis of large-scale structures. The ordinary IBS method couples the substructure impulse response functions (IRFs) with coincident interface nodes. However, the interface nodes in a practical structure are usually mismatched. This paper extends the ordinary IBS method and presents a method for coupling multi-domain substructures, including IBS, FEM and modal substructures, with non-matching interfaces. Both displacement compatibility and force equilibrium are satisfied on the non-matching interfaces of substructures by introducing the normalized interpolation technique into the framework of IBS. To evaluate the performance of the proposed method, numerical models and a practical application with a lunar lander and a rover are presented. The main bodies of the lander and the rover are coupled by non-matching interfaces, and the coupled system is excited by a buffer load. With the employment of this proposed method, the computing time of the landing simulation of the lunar lander is dramatically reduced, and the results show strong agreement with references. It is demonstrated that the proposed method is accurate and efficient in the transient dynamic analysis of engineering structures. [ABSTRACT FROM AUTHOR]

Over the last century, our societies have experienced a sharp increase in urban population and fossil-fuelled transportation, turning air pollution into a critical issue. It is therefore key to accurately characterize the spatiotemporal variability of surface air pollution in order to understand its effects upon the environment, knowledge that can then be used to design effective pollution reduction policies. Global atmospheric composition reanalyses offer great capabilities towards this characterization through assimilation of satellite measurements. However, they generally do not integrate surface measurements and thus remain affected by significant biases at ground level. In this study, we thoroughly evaluate two global atmospheric composition reanalyses, the Copernicus Atmosphere Monitoring Service (CAMSRA) and the Modern-Era Retrospective Analysis for Research and Applications v2 (MERRA-2), between 2003 and 2020, against independent surface measurements of O 3 , NO 2 , CO, SO 2 and particulate matter (PM; both PM 10 and PM 2.5) over the European continent. Overall, both reanalyses present significant and persistent biases for almost all examined pollutants. CAMSRA clearly outperforms MERRA-2 in capturing the spatiotemporal variability of most pollutants, as shown by generally lower biases (all pollutants except for PM 2.5), lower errors (all pollutants) and higher correlations (all pollutants except SO 2). CAMSRA also outperforms MERRA-2 in capturing the annual trends found in all pollutants (except for SO 2). Overall, CAMSRA tends to perform best for O 3 and CO, followed by NO 2 and PM 10 , while poorer results are typically found for SO 2 and PM 2.5. Higher correlations are generally found in autumn and/or winter for reactive gases. Compared to MERRA-2, CAMSRA assimilates a wider range of satellite products which, while enhancing the performance of the reanalysis in the troposphere (as shown by other studies), has a limited impact on the surface. The biases found in both reanalyses are likely explained by a combination of factors, including errors in emission inventories and/or sinks, a lack of surface data assimilation, and their relatively coarse resolution. Our results highlight the current limitations of reanalyses to represent surface pollution, which limits their applicability for health and environmental impact studies. When applied to reanalysis data, bias-correction methodologies based on surface observations should help to constrain the spatiotemporal variability of surface pollution and its associated impacts. [ABSTRACT FROM AUTHOR]

Objective The aim of this study was to investigate the correlations between body composition and traditional Chinese medicine (TCM) constitution in normal-weight, overweight, and obese outpatients in Department of Acupuncture for Endocrine-related Obesity. Methods The "YiJianZhong Weight Management" We Chat app was used to record patients' weight, TCM constitution (only five types of TCM constitutions were included: balanced constitution, phlegm-dampness constitution, damp-heat constitution, yang-deficiency constitution, and qi-stagnation constitution), and other information. In addition, a body composition analyzer was used to collect the information including the percentage of body fat, body mass index (BMI), basal metabolic rate, and visceral fat index. Finally, the body constitution data of patients with different TCM constitutions were summarized and analyzed. Results A total of 308 patients were included in the analysis, including 100 cases of normal-weight patients and 208 cases of obese or overweight patients. The proportions of TCM constitutions in the normal-weight patients were ranked from most to least as follows; balanced constitution > yang-deficiency constitution > damp-heat constitution > qi-stagnation constitution > phlegm-dampness constitution, while the proportions of TCM constitutions in obese and overweight patients were ranked in the same order as follows; balanced constitution > phlegm-dampness constitution > damp-heat constitution > yang-deficiency constitution > qi-stagnation constitution. There was no significant difference in the composition ratio of the different TCM constitutions between normal-weight patients and overweight, obese patients. The BMIs of all the patients were negatively correlated with the qi-stagnation constitution scores. The BMI decreased by 0.152 kg/m when the qi-stagnation constitution score increased by one point. The age and qi-stagnation constitution scores had a positive interaction with the BMI. For every 1-year increase in the average age of patients, the effect of the qi-stagnation constitution scores on the BMI changed from -0.152 kg/m to -0.147 kg/m. Conclusion In terms of the TCM constitution, a balanced constitution accounted for the highest proportion in normal-weight patients, overweight, and obese patients, while phlegm-dampness and damp-heat constitution accounted for a higher proportion in overweight and obese patients, except for the balanced constitution. In addition, in terms of the relationship between the TCM constitution and body composition, due to the negative correlation between the BMI and the qi-stagnation constitution score, overweight or obese patients with a qi-stagnation constitution should pay more attention to the influence of body composition indicators other than BMI on the development of disease. [ABSTRACT FROM AUTHOR]

Objective: To investigate the occurrence rate of the prelacrimal recess (PLR) and its medial bony wall dimensions based on the radiological analysis to help surgeons enhance the understanding of anatomic structures for the endoscopic prelacrimal recess approach. Methods: Cone-beam computed tomography images of 255 patients were evaluated retrospectively. The prevalence of the PLR in maxillary sinus was investigated and the thickness of its medial bony wall was measured and statistically assessed. Meanwhile, the width of the PLR was measured. The correlation between the width of the PLR and its medial bony wall thickness was assessed. The data were compared between the left side and right side, male and female. Results: The PLR was present in 82.5% of the maxillary sinus, with no significant differences between the left and right sides, as well as different gender groups. The mean thickness of the medial bony wall of the PLR was 2.84 ± 1.41 mm, without statistical difference between the left and right sides but significantly larger in males than in females. The mean width of the PLR was 4.62 ± 1.74 mm and it had a significant negative correlation with the thickness of the medial bony wall of the PLR. Conclusion: A large individual variation exists in the anatomy of PLR, including its prevalence and dimensions of its medial bony wall. When considering the intranasal endoscopic prelacrimal recess approach, the surgeons should carefully evaluate the anatomical structure of the PLR preoperatively so as to minimize the risks of surgical complications. [ABSTRACT FROM AUTHOR]

Purpose: Cone-beam CT dacryocystography (CBCT-DCG) is a newly developed lacrimal passage imaging technique. This pilot study aimed to determine the effect of reducing tube current on image quality and radiation dose of CBCT-DCG in healthy volunteers. Materials and methods: Thirty volunteers were randomly divided into three groups of ten. Each group of subjects underwent CBCT-DCG using a tube current of 13 mA, 10 mA, and 7 mA respectively. The image quality of CBCT-DCG was assessed independently by two observers using three different scoring methods and compared among the groups. The effective dose was estimated and compared among the three different tube current groups. Results: The CBCT-DCG images provided a high spatial and contrast resolution of the bony structures and the contrast medium. No significant differences were found in the image quality between different tube current groups. Compared with the 13 mA group (49.44 μSv), the effective dose for 10 mA group (38.40 μSv) and 7 mA group (27.12 μSv) decreased by 22.33% and 45.15%, respectively. Conclusion: By decreasing the tube current, CBCT-DCG can be performed with a significant reduction of effective dose without loss of image quality in healthy volunteers. [ABSTRACT FROM AUTHOR]

Objectives: Cone beam CT dacryocystography (CBCT-DCG) is a new imaging technique for assessing the lacrimal drainage system (LDS). The purpose of this pilot study is to compare the diagnostic capability and radiation dose of CBCT-DCG in different scanning fields of view (FOV) to evaluate the possibilities of the reduction of radiation dose. Methods: Fifteen healthy volunteers underwent CBCT-DCG in an upright position. The first five subjects were scanned using the scanning FOV of 11 × 10 cm (Group A), then 8 × 8 cm (Group B), and the last five subjects 5 × 5.5 cm (Group C). The image quality and diagnostic validity of different groups were evaluated by two experienced otolaryngologists. The effective dose of each group was calculated and compared. Results: All images showed good delineation of the LDS and its surrounding structures. With regard to the image quality and diagnostic validity, no differences were found among different groups. Compared with Group A, the effective radiation dose for Group B (38.40 μSv) was 38.54% lower and that for Group C (17.12 μSv) was 72.60% lower. Conclusions: A substantial reduction of the effective dose for CBCT-DCG in healthy volunteer by decreasing FOV is possible without compromising the diagnostic capability. CBCT-DCG is a potential valid first-line imaging test for the evaluation of LDS, and it permits functional assessment of lacrimal drainage. [ABSTRACT FROM AUTHOR]

Background: The intranasal endoscopic prelacrimal recess approach (PLRA) to the maxillary sinus (MS) has been reported to treat many MS and skull base diseases. However, previous studies revealed that the width of the prelacrimal recess (PLR) shows a large individual variation. The purpose of this study was to ascertain the prevalence of the PLR in MS according to gender and age. Methods: A series of 701 maxillofacial cone beam computed tomography (CBCT) scans from adult patients were analyzed retrospectively. Patients were divided into five age groups (18–24 years, 25–34 years, 35–44 years, 45–54 years, and ≥ 55 years) and by sex. The frequencies of occurrence of the PLR in the MS were calculated and compared. Results: According to the findings obtained from our study, PLR was present in 81.5% of maxillary sinuses. No differences were found when the data distributions of right and left sides were compared. For individuals, the right and left sides were not always symmetrical. The probability of PLR was lesser among women than among men, but this differences was not significant. Another finding of our study was that the percentage of PLR decreased with increasing age among patients aged < 55 years, however, increased again among patients aged ≥ 55 years. Conclusion: The anatomy of PLR varies among individuals. Careful analysis of individual anatomical structure characteristic is recommended when considering intranasal endoscopic PLRA to the MS. Besides, the age variation of PLR should be considered in order to avoid complications. [ABSTRACT FROM AUTHOR]

Background: Limited evidence is available on the health effects of particulate matter (PM including PM2.5 with an aerodynamic diameter ≤ 2.5 μm; PM10, ≤ 10 μm; PM2.5–10, 2.5–10 μm) during the pandemic of COVID-19 in Italy. The aims of the study were to examine the associations between all-cause mortality and PM in the pandemic period and compare them to the normal periods (2015–2019). Methods: We collected daily data regarding all-cause mortality (stratified by age and gender), and PM concentrations for 107 Italian provinces from 1 January 2015 to 31 May 2020. A time-stratified case-cross design with the distributed lag non-linear model was used to examine the association between PM and all-cause mortality. We also compared the counts and fractions of death attributable to PM in two periods. Results: Italy saw an increase in daily death counts while slight decreases in PM concentrations in pandemic period. Each 10 µg/m3 increase in PM was associated with much higher increase in daily all-cause mortality during the pandemic period compared to the same months during 2015–2019 (increased mortality rate: 7.24% (95%CI: 4.84%, 9.70%) versus 1.69% (95%CI: 1.12%, 2.25%) for PM2.5; 3.45% (95%CI: 2.58%, 4.34%) versus 1.11% (95%CI: 0.79%, 1.42%) for PM10; 4.25% (95%CI: 2.99%, 5.52%) versus 1.76% (95%CI: 1.14%, 2.38%) for PM2.5–10). The counts and fractions of deaths attributable to PM were higher in 2020 for PM2.5 (attributable death counts: 20,062 versus 3927 per year in 2015–2019; attributable fractions: 10.2% versus 2.4%), PM10 (15,112 versus 3999; 7.7% versus 2.5%), and PM2.5–10 (7193 versus 2303; 3.7% versus 1.4%). Conclusion: COVID-19 pandemic increased the vulnerability and excess cases of all-cause mortality associated with short-term exposure to PM2.5, PM2.5–10, and PM10 in Italy, despite a decline in air pollution level. [ABSTRACT FROM AUTHOR]