[en] Objective: To investigate the epidemiological characteristics of human immunodeficiency virus infected patients and the correlation between the preliminary screening results and confirmed results by analyzing the data of HIV antibody detection and confirmation results from 2012 to 2018 in Beijing Haidian hospital, so to provide a reference for the policy-making of the prevention and intervention of HIV infection. Methods: A total of 246458 patient samples from 2012 to 2018 were selected as the study objects. The samples with positive results were screened by chemiluminescence and ELISA, and confirmed by laboratory western blot (WB). The general data of positive patients were analyzed retrospectively and the test results were statistically analyzed. Results: From 2012 to 2018, a total of 246458 HIV antibody tests were completed, and 553 positive samples were screened with a positive rate of 0.22%. The confirmed positive rate was 0.14% based on 337 cases. There were also 121 negative cases and 95 uncertain cases. The age range of the confirmed positive patients was between 16 to 76 years old, among which 318 were males and 19 were females. The proportion of males was 94.36%, which was significantly higher than that of females, which was 5.64%. Clinical records were mostly distributed in dermatology outpatients, accounting for 69.44%. Conclusion: HIV virus is generally distributed with a low epidemic, with men aged 21-30 as the high-risk group. The prevention and control measures should be strengthened and a sound service system should be established. The screening of high-risk populations should be strengthened and related knowledge should be publicized, especially the education among college students, so to effectively curb the spread of AIDS. At the same time, improving detection technology to reduce the false positive rate of HIV antibody detection is of great significance for preventing and controlling HIV infection. (authors)

[en] Multivariate time series is widely used to evaluate and predict the health state of system. To focus on the importance of prediction accuracy for multivariate time series, many a research have been done on improving the performance of predictive model. However, for multivariate time series, the prediction accuracy depends not only on predictive model but also on the input information. In this paper, we combine data fusion with ESN to improve the prediction accuracy of multivariate time series, which focuses on both the processing of the input information of predictive model and the optimizing of predictive model. First, multi-sources data fusion is presented to obtain the new input for prediction model before predicting; phase space reconstruction and self-adaptive weighted fusion algorithm are adopted to fuse multivariate time series and obtain more complete information. Then, leaky rectifier liner units are used to replace the original activation function, tanh, and locality preserving projection is employed to optimize the state matrix of the reservoir. Finally, the effectiveness of the proposed method is verified by an analysis of one case study of real compressor groups data sets in chemical production system. The results and a comparison with the traditional method show that the proposed method can greatly enhance the prediction accuracy of multivariate time series and the one-step ahead prediction accuracy is improved by three orders of magnitude as well as a better generalization ability is obtained in the multi-steps ahead prediction.

[en] This paper focuses on the microstructure and martensitic transformation of titanium−nickel (Ti−Ni) alloys under electron irradiation. There is no observable change of the microstructure after irradiation. Abnormal multistage martensitic transformations are observed in Ti‐rich Ti‐48 at % Ni alloys after electron irradiation. The three‐stage reverse martensitic transformation can be achieved in the irradiated alloy, while unirradiated counterpart displays normal one‐stage transformation during heating processes. The abnormal reverse martensitic transformation behavior caused by electron irradiation is due to the local stress field and the excessive defect concentration. The martensitic transformation behavior and temperature after annealing at 250 °C are consistent with the unirradiated counterpart. Additionally, the irradiated alloy exhibits superior thermal cycle stability to unirradiated samples. (© 2020 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] The quasi-uniform three-dimensional super high pressure was employed in the Ni-rich Ni-Ti alloy during aging treatment. Moreover, the effects of aging conditions (temperature, time and pressure) on the precipitation of Ti₃Ni₄ phase, martensitic transformation behavior and mechanical properties of the alloy were investigated systematically. The results revealed that the applied of super high pressure can provide the nuclear driving force of Ti₃Ni₄ precipitate and promote the precipitation of Ti₃Ni₄ phase. Unlike the applied of the uniaxial tensile or compressive stress, no significant preferred orientation of Ti₃Ni₄ precipitate was observed in the present stress-assisted aged Ni-Ti alloys as a consequence of the quasi-uniform three-dimensional stress. In addition, a certain number of dislocations generated in the aged Ni-Ti alloys due to the applied of super high pressure. However, the variations of the martensitic transformation behavior and mechanical properties are closely related to the evolution of the precipitation of Ti₃Ni₄ phase with the aging parameters and the generation of internal stress as well as the different thermodynamic state.

[en] Highlights: • The amorphous Ti-Ni-Zr alloy ribbon was fabricated successfully. • The sequence of crystallization for Ti-Ni-Zr alloy ribbon was investigated. • The phase constitutions of annealed ribbons were dependent on the annealing temperatures. • The transformation temperatures increased with the annealing temperatures increasing. • The annealed alloy ribbon showed the superior thermal cycling stability. The rapid solidified Ti-Ni-Zr amorphous ribbon was crystallized to B2 phase and λ1 phase. The phase constitutions of Ti-Ni-Zr alloy ribbon were dependent on the annealing temperatures. The annealed ribbon with the annealing temperature of 773 K and 873 K consisted of B2 parent phase and λ₁ phase. When the annealing temperature increased to 973 K, the B19′ martensite can be introduced except from the B2 phase and λ₁ phase. With further increasing the annealing temperature to 1073 K, only B19′ martensite and λ₁ phase was observed. The transformation temperatures increased successively with the increasing of the annealing temperature, which was closely related to the variation of the phase constituents. The annealed ribbons with the moderate annealing treatment showed the higher transformation temperature and the superior thermal cycling stability.

[en] The failure of electronic equipment causes serious consequences and even catastrophic fires. Abnormal thermal signals are one of the main characteristics of the failure of electronic equipment. Thus, a new method for recognizing and predicting the thermally induced failure states of electronic equipment was proposed, based on an artificial olfactory system (AOS). The AOS recognizes the state of the volatile components released during the early stages of thermally induced failure and uses it to predict the state of health of the electronic equipment. Some typical electronic devices, such as microcomputer units, electronic rectifiers, transformers, and battery modules, were tested with the AOS to recognize the failures indicated by abnormal thermal accumulation. Compared with infrared thermal imagers and gas analyzers, the PEN3 electronic nose was utilized to monitor the status of the devices under different thermal failure scenarios. It was found that infrared thermal imaging was only able to monitor the local surface temperature, and the air temperature in the device chamber changed slowly with the surface temperature of the electronic modules. However, the AOS was able to detect the abnormal change in the whole chamber. Linear discriminant analysis (LDA) and principal component analysis (PCA) were then adopted to investigate the features of thermally induced failure for different thermal states. The results showed that the models obtained both from LDA and PCA were able to distinguish the different states of the electronic devices. Furthermore, a support vector machine model was built, based on the AOS data, to recognize and predict the thermally induced failure processes. All the failure states of the electronic devices caused by thermal simulations were recognized successfully and the prediction accuracy was above 95%. Hence, the experimental results of this research proved that using the AOS, it is feasible to predict the thermally induced failure states of electronic equipment, and the failure of electronic devices can be forecast in advance, before the obvious temperature rise and smoke release. Moreover, the method proposed in this research can also be applied to the prediction of, and warning about, electrical fires, indoor fires, and other thermally induced accidents. (paper)

[en] Propellant gas flow has an important impact on the ionization and acceleration process of Hall effect thrusters (HETs). In this paper, a particle-in-cell numerical method is used to study the effect of the anode temperature, i.e., the flow speed of the propellant gas, on the discharge characteristics of a HET. The simulation results show that, no matter the magnitude of the discharge voltage, the calculated variation trends of performance parameters with the anode temperature are in good agreement with the experimental ones presented in the literature. Further mechanism analysis indicates that the magnitude of the electron temperature is responsible for the two opposing variation laws found under different discharge voltages. When the discharge voltage is low, the electron temperature is low, and so is the intensity of the propellant ionization; the variation of the thruster performance with the anode temperature is thereby determined by the variation of the neutral density that affects the propellant utilization efficiency. When the discharge voltage is high, the electron temperature is large enough to guarantee a high degree of the propellant utilization no matter the magnitude of the anode temperature. The change of the thruster performance with the anode temperature is thus dominated by the change of the electron temperature and consequently the electron-neutral collisions as well as the electron cross-field mobility that affect the current utilization efficiency. (paper)

[en] Aiming to solve the problems of low accuracy of multi-step prediction and difficulty in determining the maximum number of prediction steps of chaotic time series, a multi-step time series prediction model based on the dilated convolution network and long short-term memory (LSTM), named the dilated convolution-long short-term memory (DC-LSTM), is proposed. The dilated convolution operation is used to extract the correlation between the predicted variable and correlational variables. The features extracted by dilated convolution operation and historical data of predicted variable are input into LSTM to obtain the desired multi-step prediction result. Furthermore, cross-correlation analyses (CCA) are applied to calculate the reasonable maximum prediction steps of chaotic time series. Actual applications of multi-step prediction were studied to demonstrate the effectiveness of the proposed model which has superiorities in RMSE, MAE and prediction accuracy because of the extraction of correlation between the predicted variable and correlational variables. Moreover, the proposed DC-LSTM model provides a new method for prediction of chaotic time series and lays a foundation for scientific data analysis of chaotic time series monitoring systems.

[en] Highlights: • The peak value of relaxation damping peak increases and then decreases with the increase of irradiation dose. • The relaxation IF increases from 0.04 to 0.055 with a wide span of temperature range after electron irradiation at 2 × 10¹⁷ e/cm². • The isothermal IF of twin boundary relaxation damping remains stable with a span of 160 ℃ (IF>0.03) from 50 ℃ to 210 ℃. -- Abstract: Damping devices need to maintain a high internal friction value in a wide high-temperature range in an aviation environment. Damping behavior is sensitive to defects including vacancies, interstitials, and dislocations. Electron irradiation is an effective method to introduce defects into materials to tailor the damping properties. The relaxation internal friction peak value increases first and then decreases with the increase of irradiation dose in Ni₅₄Mn₂₅Ga₂₁ alloy. The peak value increases from 0.04 to 0.055 by 37.5% after irradiated by 1.2 MeV electrons at 2 × 10¹⁷ e/cm². It derives from the effect of dislocations on the interaction between interstitials and twin boundaries. The high isothermal internal friction remains stable with a large working temperature range of 160 ℃ from 50 ℃ to 210 ℃. This research provides a new method to obtain high damping Ni₅₄Mn₂₅Ga₂₁ alloy with a wide high-temperature range.

[en] Highlights: → This method is simple and with well reproducibility. → Moreover it expels the usage of template in constructing the hollow structure. → This method could serve as a general route to prepare other rare earth fluorides hollow spheres. → In addition, the nano-sized hollow spheres could cut down the usage of expensive rare earth element for lower producing cost. → These well-crystallized EuF₃ nano-sized hollow spheres could be used as a promising material to fabricate light-emitting device owing to the high efficiency and thermal stability. - Abstract: Monodisperse EuF₃ hollow spheres with diameter of about 95 nm were firstly synthesized using Eu(OH)CO₃ nanospheres as template. Control experiments indicated the morphology and crystal quality of the final products were greatly influenced by the synthesis parameters such as pH value, temperature and reactant concentration. Subsequently, a possible growth mechanism for the nano-sized hollow sphere was proposed and the photoluminescence (PL) properties of as-prepared EuF₃ products were also intensively studied. Furthermore, this method could serve as a general route to prepare other rare earth fluorides hollow spheres.