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Finding out the reason of the fracture fault of tail rotor on a helicopter is of practical significance for using and maintaining the helicopter and is of significant reference for improving safety of new type helicopter. The fracture fault of tail rotor blade on a helicopter is analyzed by fault tree analysis method, and the bottom event analysis results are obtained. Then, the macro and micro fractographic analysis of the tail rotor blade is carried out. Finally,the simulation analysis of the fractographic damage evolution of flexible beam is performed. The results show that the fracture property of the blade is low-stress and high-cycle bidirectional bending fatigue fracture. When the strength value of the fiber compression direction of the flexible beam is less than 700 MPa, the fractographic type is similar to that of the faulty tail rotor flexible beam. The tail rotor will produce large vibration under large fatigue load condition, and the increase of vibration can intensify the load of the tail rotor, which leads to the increase of load at the root of the flexible beam and exceeds the designed bearing capacity of the flexible beam, then fatigue fracture will occur at the root of the flexible beam of the blade.

In this work, the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in Ti–44Al–1.2C alloys were systematically studied by observing their distribution, morphology, and interface atomic structure. The experiment results show that the needle-like C atom segregation zones in TiAl alloys are the nucleation site of Ti2AlC, and the long axis direction of segregation zones is parallel to the TiAl(111) plane. The rod-like Ti2AlC nano-precipitates mainly distribute at the TiAl/Ti3Al interface, and the orientation relationship between them is [1̅01\bar{1}01]TiAl//[112̅011\bar{2}0]Ti2AlC//[112̅011\bar{2}0]Ti3Al, (111)TiAl//(0001)Ti2AlC//(0001)Ti3Al. The needle-like Ti3AlC nano-precipitates distribute in TiAl with the orientation relationship of [001]Ti3AlC//[001]TiAl, (100)Ti3AlC//(100)TiAl, (020)Ti3AlC//(020)TiAl, and (110)Ti3AlC//(110)TiAl during the nucleation stage. After growing into the rod-like, the orientation relationship between Ti3AlC precipitates and TiAl is [11̅01\bar{1}0]Ti3AlC//[11̅01\bar{1}0]TiAl, (001)Ti3AlC//(001)TiAl, (220)Ti3AlC//(220)TiAl, and (111)Ti3AlC//(111)TiAl. Both the needle- and rod-like Ti3AlC precipitates preferentially grow along the [001]TiAl direction. The crystal structure and lattice mismatch between Ti2AlC and Ti3AlC nano-precipitates and the TiAl matrix determine their distribution, morphology, and interface atomic structure.

To attenuate low-frequency noise in square ventilation ducts, a tunable duct silencer consisting of composite Helmholtz resonators (HR) that precisely controlled by a step motor was proposed in this paper. An analytical model based on temporal coupled mode theory (TCMT) is applied to explain the sound absorption mechanism. The design breaks the limitation that the operating frequency of a silencer is fixed after manufacturing and avoids the degradation of ventilation conditions by attaching to the duct as a side branch. By using a step motor to drive the tunable cavity HR, the silencer can achieve accurate and continuous adjustment of the operating frequency over the entire operating frequency spectrum. In the experiment, the silencer has an absorption bandwidth of 250 Hz and ranges from 710 Hz to 960 Hz. Porous material is inserted into the cavities of HR to improve the damping properties. When integrated into the simulation model, it enables the rapid design of silencer dimensions for different sound absorption frequencies. The design demonstrates a new solution for low frequency sound attenuation in ventilation ducts and provides a potential technique for the future development of active controlled duct silencers.

Objective To compare the differences between the gray matter structures of amyotrophic lateral sclerosis (ALS) patients with limb-onset and bulbar-onset. Methods A total of 35 ALS patients with normal cognitive function were enrolled in Peking Union Medical College Hospital ALS Registry Platform from September 2013 to March 2018, and 20 healthy controls with matched age and education were included in the study. ALS patients were divided into limb-onset group (ALS-L group, n = 20) and bulbar-onset group (ALS-B group, n = 15) according to their clinical onset sites. Three-dimensional T1-fast spoiled gradient-recalled (3D-T1-FSPGR) of all subjects was collected. Gray matter volume of each group were compared using voxel-based morphometry (VBM). Within the compound region of interest (ROI) consisting of bilateral primary motor cortex, premotor cortex and supplementary motor area, the atrophy patterns of the motor cortex were compared between ALS-L group and ALS-B group. Results Compared with the control group, the ALS-L group had decreased gray matter volume in the left superior temporal gyrus-temporal pole (t = 3.932, uncorrected P < 0.001), left middle temporal gyrus (t = 3.836, uncorrected P < 0.001), right insula (t = 3.992, uncorrected P < 0.001). Compared with the ALS-B group, the ALS-L group had decreased gray matter volume in the right superior frontal gyrus (t = -3.158, uncorrected P < 0.001), left cingulate gyrus (t = -3.002, uncorrected P < 0.001). In the analysis of the motor cortex as ROI, the gray matter volume of the segments representing hand (t = 2.237, uncorrected P < 0.001) and lower limb (t = 2.728, uncorrected P < 0.001) of the left motor cortex in the ALS-L group was reduced significantly than that of ALS-B group. Conclusions ALS-L has more significant gray matter atrophy than ALS-B, and the local atrophy pattern of motor cortex in ALS patients corresponds to its functional disability.

Objective To evaluate the clinical and paraclinical features of Chinese patients with anti- LGI1 encephalitis. Methods Patients with memory deficits, psychiatric symptoms, seizures or altered level of consciousness, suspicious of encephalitis, at presentation to Peking Union Medical College Hospital were recruited between July 2013 and January 2018, and tested for anti-LGI1 antibodies in their serum and/or cerebrospinal fluid(CSF) samples. Patients with anti-LGI1 antibodies were enrolled. The demographic characteristics, clinical manifestations, laboratory examination results, neuroimaging features, immunotherapy, follow-up practices and outcomes for included patients were registered and analyzed. Results The study enrolled 120 patients, of whom 66.7% were male. The median age was 61 years (interquartile range [IQR]: 49-66 years). Seizures(65.0%) were the most common initial symptoms. Most patients developed seizures (95.0%), including faciobrachial dystonic seizures (54.2%), memory deficits (92.5%), and psychiatric symptoms (69.1%). Brain MRI and 18F-FDG PET / CT showed that the lesions were mainly located in unilateral or bilateral medial temporal lobes, and (or) basal ganglia. Of the patients, 95.0% received intravenous immunoglobulin (IVIg) or corticosteroids, 47.5% received mycophenolate mofetil as long-term immunotherapy, and no one received second-line immunotherapy. The median follow-up was 34.2 months(IQR: 22.0-45.6 months). 91.2% had a good outcome (modified Rankin Scale score≤2 points). Residual mild memory deficits were present in 47.8% of the patients. Nine deaths were documented. Relapses occurred in 24.8% of the patients in the first year. In total, 24 (20%)cases were young patients(onset age ≤45 years).There were fewer males among the younger patients(37.5% vs. 74.0%, P < 0.01). Besides, there were fewer younger patients with psychiatric symptoms(50.0% vs. 74.0%, P=0.02), hyponatremia(33.3% vs. 68.8%, P < 0.01), and abnormalities on brain 18F-FDG PET/CT(20.8% vs. 47.9%, P=0.02). The relapse-free survival rate was significantly higher in the young patients. Conclusions Elderly males were predominant in patients with anti-LGI1 encephalitis. Most patients developed symptoms of limbic encephalitis and/or FDBS during the disease course. Several patients were young adults and lacked typical symptoms. Neuroimaging features were consistent with the involvement of limbic system or basal ganglia. Patients with anti-LGI1 encephalitis respond well to immunotherapy, irrespective of the age.

Objective: The effect of frozen temperature on the storage characteristics of ready-to-eat snakehead sausages were investigated. Methods: In this study, The freezing temperature dehydration technique was used to control the moisture content of snakehead sausage at about 50%, and then the temperature was lowered to-5.6 ℃. Subsequently, the sausage was stored at -4 ℃, and those stored at 4 ℃ were set as the control. The changes in the quality and microstructure of the snakehead sausages were analyzed, by measuring the physicochemical indexes such as total bacterial colony, color, water holding capacity, textural properties, biogenic amines and scanning electron microscopy during storage. Results: The logarithmic values of TVC were （5.37±0.06）; TVB-N were （17±0.03） mg/100 g; the total amine mass fraction were （324.93±1.89） mg/kg at 42 d. The results of colony count and TVB-N analysis showed that, compared to those stored at 4 ℃, frozen storage could extend the shelf life of snakehead sausage by 1-fold. The low-field NMR results showed that the moisture distribution of snakehead sausage during frozen storage was better than that of the control. Scanning electron microscopy showed that the gel network of the frozen-storage group had a higher degree of binding to fat particles. The frozen storage of snakehead sausage was superior to the refrigerated storage. Conclusion: The preservation effect of snakehead sausage stored at freezing temperature is better than that of refrigerated storage.

The construction industry is characterized by long production cycles, poor mobility of workers, various kinds of outdoor operations and complex construction processes, leading to frequent safety accidents. To explore the occurrence rule of the construction accidents in building construction, this paper applied knowledge graph technology in the field of artificial intelligence to analyze construction accidents. Firstly, defining the conceptual architecture of the domain knowledge graph. Secondly, extracting key knowledge elements from construction accident data. The knowledge graph of construction accidents has been established by using the Neo4j graph database. Further, a construction accident analysis process based on the knowledge graph has been proposed. The intelligent analysis, such as query, statistical analysis and correlation path analysis for accident information have been conducted. The results shows that based on knowledge graph technology, construction accidents in visual graphics or tables could be visualized. The accident information in the form of knowledge could be saved and queried quickly. The study can provide knowledge support for accident prevention and improve the efficiency of accident analysis. Besides, it can provide innovative ideas as well as decision support for safety management.

In order to quantitatively characterize the ability of PVD(physical vapor deposition) film sensors to detect cracks in metallic structures, the process parameters applied to LY12-CZ aluminium alloys were first optimized using orthogonal tests, and coin shape, 1mm concentric dual ring shape, 0.5mm concentric tricyclic shape PVD film sensors were prepared on three groups of specimen with central hole using these parameters. Subsequently, the on-line monitoring experiment of fatigue cracks was carried out under laboratory conditions, the potential output signals of the PVD film sensors and microscope observations were compared and analysed. Finally, the probability of detection curves of all kinds of PVD thin-film sensors and PVD film sensor in different shapes were plotted separately using the improved crack size separation method and binomial distribution detection model. PVD thin-film sensors have 93.56% detection probability for cracks with length greater than 0.99mm at 95% confidence level. Compared to coin-shaped thin-film sensors, concentric ring shape film sensors are more sensitive to cracks smaller than 0.5mm, and the sensors with finer channel width have the higher probability of detection on small size cracks.

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

The fatigue life scatter factor is an important reliability index of the assessment of aircraft fatigue life. At present,the safe-life of a fleet is gotten by using the total test hours and the fatigue scatter factor. Usually,the environment scatter factor caused by the different service environments is not considered,and the fatigue scatter factor mainly includes two parts,one is the load scatter factor caused by the load spectrum difference of fleets; the other is the structure scatter factor caused by the difference of material and manufacturing quality. The expressions of scatter factor of fatigue life obeying the log-normal distribution and Weibull distribution are introduced and analyzed. To the situation that the structure fatigue life of the same aircraft model under different load spectrums obeys the log-normal distribution,the condition that the fatigue scatter factor is the product of the load scatter factor and the structure scatter factor is deduced. To the situation that the structure fatigue life obeys the different distributions,the service flying hours can be converted into the equivalent flying hours under the same test load spectrum based on the equal damage principle,the structure scatter factor under this spectrum can be calculated and can be taken as the fatigue life scatter factor,the safe-life calculated by this scatter factor can be seen as the reference value for the management of individual aircraft life.