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BACKGROUND The emerald is loved by people because of its gorgeous color and is respected as one of the world's four major gems. Due to the high value of emeralds, a variety of synthesis and optimization methods have emerged. The hydrothermal method is one of the common methods to produce synthetic emeralds. The emeralds synthesized by this method have typical water ripple texture, showing a serrated parallel arrangement, and the characteristic peaks of the infrared absorption spectrum in the range of 2300-3100cm-1 are the main identification feature. However, some emeralds synthesized by this method do not have the above typical characteristics. This has brought a great challenge to the quality inspection agencies, and brought many doubts to the majority of consumers, and affected the stability of the gem market. OBJECTIVES It is essential to study the new emerald synthesized by this new hydrothermal method. The refractive index, density, polychromatism, and infrared absorption spectrum characteristics of the tested samples are very similar to those of natural emeralds, so infrared absorption spectrum analysis cannot obtain the supporting evidence of its cause. Based on this, the gemological and spectral characteristics of the test samples were studied by ultraviolet visible spectrum, energy dispersive X-ray fluorescence spectrometry (EDXRF) and other spectroscopic means. Finally, the test samples were determined to be a new kind of emerald synthesized by the hydrothermal method. METHODS The refractive index, birefringence, relative density, polychromaticity and weight of the samples were tested by refractometer, electronic balance, and dichroic mirror. The internal and external characteristics of the test samples, the cutting and polishing quality of the samples, and the characteristics of internal inclusions were observed by gem microscope. The infrared reflection spectrum and infrared transmission spectrum characteristics of the samples were analyzed by Fourier transform infrared spectrometer and compared with the infrared spectrum characteristics of emeralds from different origins. The absorption spectrum characteristics of the samples were analyzed by ultraviolet-visible spectrometer, focusing on the absorption peak characteristics near 830nm. The element characteristics of the samples were tested by EDXRF, because the content characteristics of Cr and Ni in emerald are the key to identify whether it is natural or not. RESULTS The mass of the tested samples was 0.17-0.56g, the refractive index was 1.571-1.588, the birefringence was 0.007-0.009, the relative density was 2.56-2.78, and the polychromaticity was obviously blue-green/green. These conventional gemological characteristics were consistent with natural emeralds. The samples were observed under a gemstone microscope, and the samples had a parallel texture of suspected water ripple, but not typical. The water ripple texture of the typical hydrothermal synthetic emeralds was serrated parallel arrangement. However, the characteristics under the gem microscope should arouse the suspicion of jewelry inspectors.The infrared reflectance spectra of the samples had characteristic peaks of 1242, 1219, 1022, 968, 810, 741, 687, 594, 528, 490, and 459cm-1. The characteristic peaks of 1242, 1219, 1022, 968, 810, 741, and 687cm-1 were caused by the stretching vibration of Si—O—Si and O—Si—O, and the characteristic peaks of 594, 528, 490, and 459cm-1 were caused by the bending vibration of Si—O and the vibration of M—O. The infrared reflection spectrum characteristics of the samples were consistent with the infrared spectrum characteristics of beryl, but the infrared spectrum characteristics of the fingerprint area could not indicate whether the samples were natural or synthetic.The infrared transmission spectra of the samples had 5445, 5273, 5109, 4874, 4800, 4650, 4547, 3321, 3222, 3027, 2953, 2928, and 2431cm-1 characteristic peaks. 5273cm-1 was caused by typeⅡ water absorption, 5445cm-1 and 5109cm-1 were caused by typeⅠ water absorption. The typeⅡ water absorption peak of the test samples was relatively sharp at 5273cm-1, and the typeⅠ water absorption peaks at 5445cm-1 and 5109cm-1 were relatively strong. Compared with previous studies, the shape and intensity of water absorption peaks of natural emerald and hydrothermally synthesized emerald were different. The infrared absorption spectrum characteristics of the water of the test sample were different from those of natural emerald, but the diagnostic direct evidence could not be obtained from the infrared absorption spectrum. The infrared peak in the range of 2300-3100cm-1 is caused by Cl- ion absorption. According to the results of previous studies, the absorption intensity of hydrothermal synthetic emeralds in this wavenumber range was significantly stronger than that of natural emeralds. The infrared absorption spectra of the test samples were relatively weak in the range of 2300-3100cm-1, which was more similar to the infrared absorption spectrum characteristics of natural emeralds in Colombia, Yunnan, Madagascar and Brazil, and was obviously different from the infrared absorption spectrum results of emeralds synthesized by the hydrothermal method. There were obvious differences between the infrared transmission absorption spectra of the traditional hydrothermal synthetic emeralds and natural emeralds. The characteristics of infrared absorption spectra are important evidence for identifying the genesis of emeralds. However, it is difficult to obtain the final accurate conclusion from the infrared absorption spectrum analysis of the test samples described in this paper, so they have been named 'new' type.The UV-Visible spectrum characteristics of the test samples showed that the absorption peak below 350nm was caused by the Fe2+-O2- charge transfer band in emerald, the absorption peak at 429nm was caused by Cr3+ ions, the broad absorption band at 550-650nm was mainly caused by Cr3+ ions, the absorption peak at 683nm was caused by Cr3+ ions, the sharp absorption peak at 956nm was caused by water absorption, and the broad absorption peak near 850nm should be caused by Fe2+ absorption, which was rarely seen in the previous hydrothermal synthesis of emerald. The combination of Cr3+ and Fe3+ replacing Al3+ makes emerald, green. The absorption peak of UV-Visible spectrum caused by Fe2+ in natural emerald was in the range of 810-850nm, and only a few of the absorption bands caused by Fe2+ in natural emeralds are not obvious. The absorption band of the UV-Visible spectra of the test samples was not obvious or weak in the range of 810-850nm, and the 850nm absorption peak of individual samples was obvious. Therefore, the emeralds examined by ultraviolet-visible spectroscopy may be synthetic, but this could not be conclusively confirmed.The EDXRF results showed that the samples had Fe, Ni and Cr elements, which was different from previous studies of natural emeralds. Yang Zhuo(2010) studies showed that the main trace elements in natural emeralds, from different origins such as Brazil, Colombia, Egypt, India, South Africa, Zimbabwe and Canada by LA-ICP-MS, were Fe, V, Cr, Mg, Na and Cs, but the content of Ni was very low, far lower than that of Cr. The content of Cr in Yunnan emeralds was 58-177μg/g, and Ni was not detected (Bai et al., 2019). The chemical element characteristics of gem-grade emeralds in Afghanistan, Brazil, Colombia, Ethiopia, Madagascar, Russia, Zambia and Zimbabwe showed that Ni element was not detected (Karampelas et al., 2019). The elemental composition of emeralds from South Africa, Afghanistan, Australia, Colombia, Egypt, Madagascar, Zambia, Zimbabwe, Tanzania and China was analyzed by electron probe microanalysis, and Ni was not detected (Lum et al., 2016). It could be seen that Cr and Fe elements coexisted in natural emeralds, but Ni was almost non-existent. EDXRF was used in this study without quantitative analysis but calibrated by the gold standard sample, and the relative peak intensity of the element was of great significance. The peak intensity of the Ni element in the test sample was much higher than that of the Cr element, which did not conform to the element content characteristics of the natural emerald, and was consistent with the high content of Ni in the hydrothermal synthesis of emerald reported by Lu and Shen (2021) and Yang et al.(2022). The comprehensive analysis showed that the test sample was a synthetic emerald. CONCLUSIONS The infrared absorption spectrum characteristics of the test samples are similar to those of natural emeralds, and the infrared absorption spectrum could not be used as a basis for identifying the genesis of emeralds. Previous studies show that a set of absorption peaks in the range of 2300-3100cm-1 in the infrared absorption spectrum is an important identification feature of the hydrothermal synthesis of emeralds, but this feature is not obvious in the tested samples. The UV-Visible spectrum of the sample shows that the absorption band near 810-850nm related to Fe2+ is not obvious. The X-ray fluorescence spectra of the samples show that the Kα peak intensity of Ni is much higher than that Kα of Cr, which is the main feature of the new emerald synthesized by the hydrothermal method. It could be seen from the experimental results that the identification of jewelry and jade is a systematic work. It is necessary to learn from the previous results and combine the comprehensive analysis of various detection methods to obtain the correct result.

Aiming at the problem that the lack of accurate and efficient off-topic detection model for current Automated English Scoring System in China, an unsupervised off-topic essay detection model based on hybrid semantic space was proposed. Firstly, the essay and its essay prompt are respectively represented as noun phrases by using a neural-network dependency parser. Secondly, we introduce a method to construct a hybrid semantic space. Thirdly, we propose a method to represent the noun phrases of the essay and its prompt as vectors in hybrid semantic space and calculate the similarity between the essay and its prompt by using the noun phrase vectors of them. Finally, we propose a sort method to set the off-topic threshold so that the off-topic essays can be identified efficiently. The experimental results on four datasets totaling 5000 essays show that, compared to the previous off-topic essay detection models, the proposed model can detect off-topic essays with higher accuracy, and the accuracy rate over all essay data sets reaches 89.8%.

Kadsura coccinea (Lem.) A. C. Smith, an evergreen liana, is widely cultivated in China for its economic importance in traditional medicine. Many phytochemical studies on the stems and roots of K. coccinea have shown numerous biological activities, such as anti-tumor, anti-HIV, and anti-oxidant (Yang et al. 2020). In June 2019, an anthracnose on K. coccinea was observed in a plantation in Longan (23°03´N, 107°54´E), Guangxi province. Disease incidence was up to 30% in a plantation. Its symptoms began as small brown spots that expanded into nearly circular spots (Fig. 1A). To isolate pathogen, diseased leaves were collected. The leaves were sterilized with 75% ethanol for 15 s followed by 2% sodium hypochlorite for 90 s, then rinsed three times in sterilized distilled water, cut into 5 × 5 mm pieces, and placed into potato dextrose agar (PDA) plates. The plates were incubated in an incubator at 25°C in dark for 2-3 days. Fungal colonies with similar morphology of 27 isolates were isolated from the 30 infected tissues. Six representative isolates (YB1 to YB6) were selected to further study their characterization. Fungal colonies were grayish-white, orange-yellow conidial masses could be observed in colonies (Fig. 1C). The mature conidia were colorless and transparent, elliptical, and single-celled, 13.0-21.0 × 4.0-8.0 μm (average 16.92 × 5.92 µm; n =100) (Fig. 1B). The DNA sequences of ribosomal internal transcribed spacer region (ITS), glyceraldehyde-3-phosphate (GAPDH), calmodulin (CAL), actin (ACT), chitin synthase (CHS-1) and β-tubulin (TUB2) were amplified by PCR using the primer pairs ITS1/ITS4, GDF/GDR, CL1C/CL2C, ACT-512F/ACT-783R, CHS-79F/CHS-354R, and T1/Bt2b (Wang et al. 2020), respectively. Sequences were submitted to GenBank (Accession nos. MZ040489 to MZ040494 for ITS, MZ069043 to MZ069048 for GAPDH, MZ069049 to MZ069054 for CAL, MZ069055 to MZ069060 for ACT, MZ069061 to MZ069066 for CHS-1, and MZ069067 to MZ069072 for TUB2). These sequences were 98%-100% identical to that of reference isolates JX010278, JX010019, JX009709, GQ856775, GQ856730, and JX010410 of Colletotrichum siamense CBS 125378 ex-type recorded in GenBank. Phylogenetic analysis of combined ITS, GAPDH, CAL, ACT, CHS-1, TUB2 genes with 16 sequences obtained from GenBank using maximum likelihood method showed that the six isolates clustered with two reference isolates of Colletotrichum siamense as a distinct clade (Fig. 2). Based on morphological characteristics and phylogenetic analysis, six isolates were identified as C. siamense . Pathogenicity tests were performed on young, fully expanded leaves of 1-year seedlings. Every leaf was punctured at 6 points on the right half and 6 points on the left half using a sterile needle. A 10 μl conidial suspension (1×10 6 conidia/ml) was inoculated on each wound on the left-half leaf and a 10 μl sterile water was inoculated on each wound on the right-half leaf (control). Each treatment was repeated three times. Inoculated leaves were wrapped in plastic bags for 2 days and after removing the bags, plants were maintained in a growth chamber at 28°C, 80% relative humidity, and a 12-h photoperiod. Anthracnose spots formed 2 to 3 days after inoculation, whereas the control leaves remained symptomless. Morphological characters matched the descriptions of C. siamense . The pathogen was previously reported to cause anthracnose on Aloe vera (Azad et al. 2020), postharvest anthracnose in mango (Liu et al. 2017), pod rot in cacao (Serrato-Diaz et al. 2020). To our knowledge, this is the first report of anthracnose on K. coccinea caused by C. siamense in China.

To study the relationship between performance changes and nanoparticles migration of the composite film at different migration stages, the poly (lactic acid) (PLA)/nano-TiO 2 composite film treated by high pressure was immersed in 50% ( v / v ) ethanol solution for 45 days at 40 °C, and the film characteristics and migration behavior were analyzed. The results showed that the migration of the composite film with the highest loading of nano-TiO 2 (20 wt. %) in alcoholic food simulated solution was far less than 10 mg/kg during the 45-day migration process. Although with the increase of migration time, the micro-morphology of composite film became rougher, the crystallinity decreased and the gas permeability increased, but the internal crystal structure of the composite film remained basically unchanged. The PLA/nano-TiO 2 composite films treated by high pressure treatment were relatively stable, and had good performance and migration behavior in alcoholic food simulated solution, the nanocomposite film after high pressure treatment could be used to reduce nano-TiO 2 particle migration and subsequently reduce human exposure as the packaging film for the packaging of alcoholic food, which provide a theoretical basis for the applications of high pressure treatment of PLA/nano-TiO 2 composite films in food packaging material and broaden its application prospects., Competing Interests: The authors declare no conflict of interest.

The microstructure, thermal properties, mechanical properties and oxygen and water vapor barrier properties of a poly(lactic acid) (PLA)/nano-TiO₂ composite film before and after high pressure treatment were studied. Structural analysis showed that the functional group structure of the high pressure treated composite film did not change. It was found that the high pressure treatment did not form new chemical bonds between the nanoparticles and the PLA. The micro-section of the composite film after high pressure treatment became very rough, and the structure was depressed. Through the analysis of thermal and mechanical properties, high pressure treatment can not only increase the strength and stiffness of the composite film, but also increase the crystallinity of the composite film. Through the analysis of barrier properties, it is found that the barrier properties of composite films after high pressure treatment were been improved by the applied high pressure treatment.