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Radio frequency fingerprint (RFF) identification is a promising technique for identifying Internet of Things (IoT) devices. This paper presents a comprehensive survey on RFF identification, which covers various aspects ranging from related definitions to details of each stage in the identification process, namely signal preprocessing, RFF feature extraction, further processing, and RFF identification. Specifically, three main steps of preprocessing are summarized, including carrier frequency offset estimation, noise elimination, and channel cancellation. Besides, three kinds of RFFs are categorized, comprising I/Q signal-based, parameter-based, and transformation-based features. Meanwhile, feature fusion and feature dimension reduction are elaborated as two main further processing methods. Furthermore, a novel framework is established from the perspective of closed set and open set problems, and the related state-of-the-art methodologies are investigated, including approaches based on traditional machine learning, deep learning, and generative models. Additionally, we highlight the challenges faced by RFF identification and point out future research trends in this field.

Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60-100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications.

Objective: To establish the quality standard for the compatibility solution of Alpinia officinarum Pogostemon cablin. Methods: Thin layer chromatography was used for qualitative identification for the two indicator components of galangin and pogostone in the compatibility solution of Alpinia officinarum Pogostemon cablin: the mixture of anpetroleum ether ethyl acetate (5:3), (5:1)as the developing solvent system on silica gel G thin layer plate, high efficiency silica gel G thin layer plate; High performance liquid chromatography was used to determine the content of galangin and pogostone: C18 chromatographic column (4.6 mmx250 mm, 5 μm)was used, and the mobile phase was methanol (A) 0.2% phosphoric acid (B), with a detection wavelength of 310 nm and gradient elution. Results:For the two indicator components of galangin and pogostone in the compatibility solution of Alpinia officinarum Pogostemon cablin, the fluorescent spots were clear, without interference from negative controls; Mass concentration was between 10.00-1 000.00 μg/mL and 10.00-640.00 μg/mL, and the linear relationship coefficients with peak area within the range of were R²= 0.999 0, R²= 0.999 9, respectively; The precision RSD was 0.63% and 0.56%, the stability RSD was 1.82% and 0.24%, and the repeatability RSD was 1.30% and 0.89%; The average recovery rates (n=9) were 103.19% (RSD=0.93%) and 100.87% (RSD=0.4%), respectively; The content of these two indicator components should not be less than 233.71 μg/mL and 61.48 μg/mL. Conclusion: A research method has been established for the quality standard of Alpinia officinarum Pogostemon cablin compatibility solution. The precision, accuracy, stability, and repeatability of this method meet the requirements. [ABSTRACT FROM AUTHOR]

Water and fertilizer integration technology can effectively improve nutrient utilization efficiency. However, the existing water and fertilizer machines have some shortcomings, such as huge cost, single fertilizer injection, need for cleaning water and so on, which hinder the development of water and fertilizer integration technology. Aiming at the problems of precise and low-cost compounding of compound fertilizer at the local farm, the water and fertilizer integrated intelligent irrigation and fertilization system were taken as the research object. In this research, new concept of an intelligent sensing system was proposed， and accurate proportioning system of water and fertilizer concentration was constructed and implemented. Firstly, a fast on-line method of intelligent sensing model of water and fertilizer was established based on a series of concentration gradient compound fertilizer solutions. The conductivity values of these formulated solutions were tested by contactless conductivity detection electrodes. Subsequently, the data analysis algorithms were discussed and compared to fit regression model. Based on the intelligent sensing model of water and fertilizer , the framework structure of in-situ intelligent sensing and accurate proportioning system of water and fertilizer concentration was designed, and the working principle of the system was also explained. The system proposed includs a first-level water and fertilizer concentration intelligent perception model building subsystem and a second-level water and fertilizer accurate proportioning subsystem. The first-level subsystem was designed as a portable device, which mainly included a precise pump for quantitative dosing, a large-range online conductivity sensor, a plastic bucket and supporting control and model building software. The second-level subsystem was designed as a dynamic and precise fertilizer distribution device. The effectiveness of the system was verified by three types of water intelligent fertilizer application so as to guide the in-situ water and fertilizer concentration ratio. The testing results showed that the second-order polynomial fitting curve under regularization conditions was the best model to express the relationship between the conductivity and the concentration of water and fertilizer, and the correlation coefficients R2 was higher than 0.999. Combined with the proportion of each index of compound fertilizer, the concentration of each index of compound fertilizer that the user cares about can be obtained according to this model. The results of three types of water intelligent fertilizer application showed that the conductivity of natural water had an effect on the water and fertilizer system, and the relative deviation was more than 0.1. The online water and fertilizer perception and ratio system proposed in this research realized the elimination of the interference of the local water conductivity on the accuracy of the ratio of water and fertilizer, and the accurate calculation of compound fertilizer was achieved through model calculation. This system has a simple structure and accurate ratio, low cost， and can be easily combined with the existing water and fertilizer integrated machine or artificial fertilizer system. The system could be widely used in facility agriculture, orchard cultivation and field cash crop cultivation, et al.

Objective To investigate the glucose metabolic status in patients with previous gestational diabetes mellitus (GDM) in the 5-6 years after delivery, and to explore the changes in insulin resistance and islet β cell function from postpartum short-term (6-12 weeks) to the long-term (5-6 years) after delivery, as well as the relationship with glucose metabolic status. Methods A total of 72 patients with a history of GDM who delivered in Peking University First Hospital and had complete short-and long-term postpartum follow-up data were included. They were divided into normal glucose metabolism (NGT) and abnormal glucose metabolism (AGT) groups according to their glucose metabolism status in 5-6 years after delivery. Pre-pregnancy, pregnancy, perinatal, short-and long-term postpartum clinical data were collected and compared between the two groups, including demographic indicators, glucose and lipid metabolism indicators [oral glucose tolerance test (OGTT) fasting blood glucose (FPG), 1-hour blood glucose (1hPG), 2-hour blood glucose (2hPG), 3-hour blood glucose (3hPG), total cholesterol, triglycerides (TG), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol], insulin use ratio, fasting insulin (FINS), OGTT 2-hour insulin (2hINS), insulin sensitivity index (ISI), homeostasis model assessment of insulin resistance index (HOMA-IR) and homeostasis model assessment of β cell function index (HOMA-β) were calculated. The comparison between the two groups was conducted using independent sample t-test, rank sum test χ² test or Fisher's exact probability test. Multivariate logistic regression analysis was used to analyze the influence factors of abnormal glucose metabolism. Results There were 38 (52.78%) cases in NGT group and 34 (47.22%) cases in AGT group. Compared with the NGT group, there are differences in related metabolic indicators in AGT group from pregnancy to long-term postpartum period: During pregnancy, 3hPG in 75 g OGTT and the proportion of insulin users were higher in AGT group. As for 6-12 weeks postpartum, OGTT 2hPG and the incidence of blood glucose abnormalities and the proportion of hypertriglyceridemia were higher (all P<0.05). However, there was no statistically significant difference in HOMA-IR and HOMA-β between the two groups(P>0.05). At 5-6 years postpartum, FPG, OGTT 2hPG, and FINS were all higher, with a higher degree of insulin resistance and lower insulin sensitivity (ISI) in AGT group (all P<0.05). Compared with short-term postpartum period (6-12 weeks), FPG, FINS, HOMA-IR, HOMA-β were all significantly increased regardless of glucose metabolic status at 5-6 years postpartum, while OGTT 2hPG and 2hINS increased further in the AGT group (all P<0.05). OGTT 2hPG and insulin use during pregnancy were risk factors for abnormal glucose metabolism 5-6 years postpartum according to multivariate logistic regression analysis, with OR values (95%CI) of 1.646 (1.015-2.671) and 3.570 (1.009-12.624), respectively. Conclusions The incidence of AGT was still high in patients with previous GDM 5-6 years after delivery. Insulin resistance progressed gradually after delivery regardless of glucose metabolism, especially in patients with abnormal glucose metabolism. OGTT 2hPG and insulin use in pregnancy were risk factors for abnormal glucose metabolism in postpartum 5-6 years, suggesting that there is continuity in time and similarity in pathogenesis between GDM and T2DM. [ABSTRACT FROM AUTHOR]