Interlamellar-Spacing Engineering of Stable and Toxicity-Reduced 2D Perovskite Single Crystal for High-Resolution X-ray Imaging.

Two-dimensional (2D) lead halide perovskites are excellent candidates for X-ray detection due to their high resistivity, high ion migration barrier, and large X-ray absorption coefficients. However, the high toxicity and long interlamellar distance of the 2D perovskites limit their wide application in high sensitivity X-ray detection. Herein, we demonstrate stable and toxicity-reduced 2D perovskite single crystals (SCs) realized by interlamellar-spacing engineering via a distortion self-balancing strategy. The engineered low-toxicity 2D SC detectors achieve high stability, large mobility-lifetime product, and therefore high-performance X-ray detection. Specifically, the detectors exhibit a record high sensitivity of 13488 µC Gy1- cm-2, a low detection limit of 8.23 nGy s-1, as well as a high spatial resolution of 8.56 lp mm-1 in X-ray imaging, all of which are far better than those of the high-toxicity 2D lead-based perovskite detectors. These advances provide a new technical solution for the low-cost fabrication of low-toxicity, scalable X-ray detectors.

Heterointerface Design of Perovskite Single Crystals for High-Performance X-Ray Imaging.

Metal halide perovskite single crystals (MHP-SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility-lifetime products and strong X-ray absorption, they are considered promising materials for efficient X-ray detection. However, they suffer from large dark currents and severe ion migration, which limit their sensitivity and stability in critical X-ray detection applications. Herein, a heterointerface design is proposed to reduce both the dark current and ion migration by forming a heterojunction. In addition, the carrier transport performance is significantly improved using heterointerface engineering by designing a gradient band structure in the SCs. The SC heterojunction detectors exhibit a high sensitivity of 3.98 × 105 µC Gyair -1 cm-2 with a low detection limit of 12.2 nGyair s-1 and a high spatial resolution of 10.2 lp mm-1 during imaging. These values are among the highest reported for state-of-the-art MHP X-ray detectors. Moreover, the detectors show excellent stability under continuous X-ray irradiation and maintainclear X-ray imaging after 240 d. This study provides novel insights into the design and fabrication of X-ray detectors with high detection efficiency and stability, which are beneficial for developing inexpensive, high-resolution X-ray imaging equipment.

The relationship between cumulative family risk and athlete burnout among Chinese college athletes: the mediating role of negative affect.

Introduction: Burnout of college athletes affects the sports performance of college athletes, etc., and plays an important role in the career development of college athletes. China attaches great importance to the mental health development of college athletes, but the influence mechanism of college athlete burnout has not received attention. This study explored the relationship between cumulative family risk, negative affect, and athlete burnout in college athletes. Methods: Data on 824 college athletes from more than 40 universities in China were collected through convenient sampling, using questionnaires including Cumulative Family Risk Scale, Athlete Burnout Questionnaire, and Negative Affect Scale. Results: The results of the structural equation model show that cumulative family risk has a significant positive effect on college athlete burnout. Cumulative family risk has a significant positive effect on the negative affect of college athletes. Negative affect also plays a significant mediating role in the relationship between cumulative family risk and college athlete burnout. Discussion: These results suggest that cumulative family risk directly or indirectly affects collegiate athlete burnout.

The Relationship between Stress Perception and Problematic Social Network Use among Chinese College Students: The Mediating Role of the Fear of Missing Out.

Based on the interaction of person-affect-cognition-execution model, this study examined the association between stress perception and problematic social network use among Chinese college students and explored the mediating effect of the fear of missing out (FoMO) on the relationship between stress perception and problematic social network use. A questionnaire survey was conducted among 554 students from nine universities in China. We found that stress perception was significantly positively correlated with problematic social network use and FoMO (r = 0.38, 0.46; p < 0.001), and FoMO was significantly positively correlated with problematic social network use (r = 0.45, p < 0.001). FoMO mediated the relationship between stress perception and problematic social network use. Conclusion: Stress perception has a negative impact on college students' problematic social network use via the mediating effect of FoMO. Practical implications that reveal the college students' problematic social network use were discussed as well.

Interlayer-Spacing Engineering of Lead-Free Perovskite Single Crystal for High-Performance X-Ray Imaging.

Lead-free A3 Bi2 I9 -type perovskites are demonstrated as a class of promising semiconductors for high-performance X-ray detection due to their high bulk resistivity and strong X-ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c-axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A-site cation of aminoguanidinium (AG) with all-NH2 terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG3 Bi2 I9 single crystals (SCs) render shorter interlamellar distance for a larger mobility-lifetime product of 7.94 × 10-3  cm2  V-1 , which is three times higher than the value measured on the best MA3 Bi2 I9 SC (2.87 × 10-3  cm2  V-1 ). Therefore, the X-ray detectors fabricated on the AG3 Bi2 I9 SC exhibit high sensitivity of 5791 uC Gy-1  cm-2 , a low detection limit of 2.6 nGy s-1, and a short response time of 690 µs, all of which are far better than those of the state-of-the-art MA3 Bi2 I9 SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lp mm-1 ) X-ray imaging. This work will facilitate the development of low-cost and high-performance lead-free X-ray detectors.

Antagonistic Activity and Mechanism of Bacillus subtilis XZ16-1 Suppression of Wheat Powdery Mildew and Growth Promotion of Wheat.

Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most serious wheat diseases in the world. Biological control is considered an environmentally safe approach to control plant diseases. Here, to develop effective biocontrol agents for controlling wheat powdery mildew, antagonistic strain XZ16-1 was isolated and identified as Bacillus subtilis based on the morphological, biochemical, and physiological characteristics and 16S rDNA sequence. The culture filtrate of B. subtilis XZ16-1 and its extracts had a significant inhibitory effect on the spore germination of Bgt. Moreover, the therapeutic and prevention efficacy of the 100% culture filtrate on wheat powdery mildew reached 81.18 and 83.72%, respectively, which was better than that of chemical fungicide triadimefon. Further antimicrobial mechanism analysis showed that the XZ16-1 culture filtrate could inhibit the development of powdery mildew spores by disrupting the cell membrane integrity, causing reductions in the mitochondrial membrane potential, and inducing the accumulation of reactive oxygen species in the spores. Biochemical detection indicated that XZ16-1 could solubilize phosphate, fix nitrogen, and produce hydrolases, lipopeptides, siderophores, and indole-3-acetic acid. Defense-related enzymes activated in wheat seedlings treated with the culture filtrate indicated that disease resistance was induced in wheat to resist pathogens. Furthermore, a 106 CFU/ml suspension of XZ16-1 increased the height, root length, fresh weight, and dry weight of wheat seedlings by 77.13, 63.46, 76.73, and 19.16%, respectively, and showed good growth-promotion properties. This study investigates the antagonistic activity and reveals the action mechanism of XZ16-1, which can provide an effective microbial agent for controlling wheat powdery mildew.

Human Umbilical Cord-Derived Mesenchymal Stromal Cells Improve Left Ventricular Function, Perfusion, and Remodeling in a Porcine Model of Chronic Myocardial Ischemia.

UNLABELLED: : Stem cell therapy has emerged as a new strategy for treatment of ischemic heart disease. Although umbilical cord-derived mesenchymal stromal cells (UC-MSCs) have been used preferentially in the acute ischemia model, data for the chronic ischemia model are lacking. In this study, we investigated the effect of UC-MSCs originated from Wharton's jelly in the treatment of chronic myocardial ischemia in a porcine model induced by ameroid constrictor. Four weeks after ameroid constrictor placement, the surviving animals were divided randomly into two groups to undergo saline injection (n = 6) or UC-MSC transplantation (n = 6) through the left main coronary artery. Two additional intravenous administrations of UC-MSCs were performed in the following 2 weeks to enhance therapeutic effect. Cardiac function and perfusion were examined just before and at 4 weeks after intracoronary transplantation. The results showed that pigs with UC-MSC transplantation exhibited significantly greater left ventricular ejection fraction compared with control animals (61.3% ± 1.3% vs. 50.3% ± 2.0%, p < .05). The systolic thickening fraction in the infarcted left ventricular wall was also improved (41.2% ± 3.3% vs. 46.2% ± 2.3%, p < .01). Additionally, the administration of UC-MSCs promoted collateral development and myocardial perfusion. The indices of fibrosis and apoptosis were also significantly reduced. Immunofluorescence staining showed clusters of CM-DiI-labeled cells in the border zone, some of which expressed von Willebrand factor. These results suggest that UC-MSC treatment improves left ventricular function, perfusion, and remodeling in a porcine model with chronic myocardial ischemia. SIGNIFICANCE: Ischemic heart disease is the leading cause of death worldwide. Many patients with chronic myocardial ischemia are not suitable for surgery and have no effective drug treatment; they are called "no-option" patients. This study finds that umbilical cord-derived mesenchymal stromal cells transplanted by intracoronary delivery combined with two intravenous administrations was safe and could significantly improve left ventricular function, perfusion, and remodeling in a large-animal model of chronic myocardial ischemia, which provides a new choice for the no-option patients. In addition, this study used clinical-grade mesenchymal stem cells with delivery and assessment methods commonly used clinically to facilitate further clinical transformation.

[Miniature near-infrared fibre optic spectrometer for the quantitative detection of protein and fat in milk powder].

The method based on miniature near-infrared spectrometer combined with Y fiber optic probe to detect the protein and fat in milk powder by diffuse reflectance spectroscopy in the wavelength range of 900-1 700 nm was proposed. By selecting the appropriate spectral bands, the correction models of protein and fat were established with partial least squares algorithm using Unscrambler 9.7 Chemometrics software. The determination coefficients R2 of the correction modes are 0.987 and 0.986 for protein and fat respectively, and the root mean square errors RMSEC are 0.385 and 0.419 respectively. Using these correction models to predict the protein and fat contents with 30 sets of forecast sample data, the prediction standard deviation is SEP(Protein) = 0.751 for protein, and is SEP(Fat) = 1.109 for fat. The results indicate that these correction models have prediction capability with unknown samples and meet the on line requirements.

[Research on the near-infrared spectrometer system].

Near-infrared spectrometer is the integration of spectrum test technology, stoichiometry technology and computer technology. In the present paper, based on effective food ingredients and non-invasive quantitative detection, the development process of the micro-near-infrared spectrometer system was introduced. Spectrometer is the basis of the system. This paper focuses on the development of the micro-near-infrared spectrometer applicable to on-line real-time testing. A micro-near-infrared spectrometer prototype was developed successfully, its main technical parameter was tested, and the result shows: its operating wavelength is: 850-1 690 nm, optical resolution is: less than 10 nm, and its performance has achieved the level of the congener foreign products. Stoichiometric technology and computer technology is the core of the system. LS-LWR modeling methods were proposed. Finally, the quantitative test for glucose water solution using the micro-near-infrared spectrometer shows that the correlation coefficient of prediction model is 0.995, and the corresponding RMSEP is 0.06.

[Model transfer method based on support vector machine].

The model transfer is a basic method to build up universal and comparable performance of spectrometer data by seeking a mathematical transformation relation among different spectrometers. Because of nonlinear effect and small calibration sample set in fact, it is important to solve the problem of model transfer under the condition of nonlinear effect in evidence and small sample set. This paper summarizes support vector machines theory, puts forward the method of model transfer based on support vector machine and piecewise direct standardization, and makes use of computer simulation method, giving a example to explain the method and compare it with artificial neural network in the end.

[Microbiochemical analyzer based on continuous spectrum and its test for clinic use].

A microbiochemical analyzer based on continuous spectrum and its test for clinic use are introduced. The principle of splitting behind was adopted to design the micro biochemical analyzer, which has the characteristics of little disorder light, real time collection of continuous spectrum signal (340-770 nm), small volume, light weight, small wastage of sample and reagent and rapidness and direct view of check. It has wide application in the emergency treatment, middling and small hospitals, rescue of battleground, and medicinal research. Representative items for clinic test were selected, such as uric acid, total cholesterin and albumin in our experiments. Comparative test and analysis of the daily check-up samples were made respectively by our microbiochemical analyzer and by the standard one of the hospital (Olympus AU2700, RT-1904C, Beckman LX-20). The test results show that our micro biochemical analyzer can meet the requirement of clinic use.

[Application of fractal theory to spectral signal recognition].

The fractal theory is a discipline that studies a kind of irregular and chaotic object with similarity of its part and whole. The fractal dimension is a basic index mark of irregularity and self-similarity in the fractal theory. The present paper takes the spectral signal according with Lambert-beer' law as the object, introduces the basic theory of fractal geometry in brief, puts forward the method of fractal dimension as the feature of spectral signal recognition, makes use of reconstructing phase space to gain the fractal dimension of spectral signal, compares different values of the fractal dimension to recognize different spectral signal, and gives an example for explanation.

[Reducing the influence non-linearity of detecting array on absorption spectrum with curve fitting].

In a micro spectral analytical system, the non-linearity response of the photoelectronic detecting array pixel will cause the deformation of the spectrum, especially in the measurement of absorption spectrum. In this paper, the factors that cause the deformation were studied and a corresponding solution was proposed to reduce such deformation. By using curve fitting, the non-linearity of the pixel can be corrected. This method was adopted to correct the absorption spectrum obtained by a micro spectral analytical system and the result showed that it is a efficient way to correct the non-linearity in the pixel of photoelectronic detecting array.