ABSTRACT Vanadium dioxide (VO2) is a typical representative of the strongly correlated electronic system. It presents a reversible first-order metal-insulator transition once stimulated by temperature, voltage, light, or pressure. The insulation-metal phase transition (MIT) makes it a new type of functional material with excellent potential applications in many fields. In this paper, magnetron sputtering technology and the "two-step method" process are used to prepare the VO2 films with phase transition properties. The results show that after the classic V film is processed for more than 100 minutes in air, and annealed in N2 atmosphere for 150 minutes, the VO2 (M) can be obtained with a resistance change rate more than three orders of magnitude. The study of the resistance change under the action of temperature and voltage found that the temperature of the heating and cooling phase transition are 67.4ºC and 62.8ºC respectively, and the hysteresis width is 4.6ºC. The relationship between phase transition voltage and ambient temperature is presented based on the heat dissipation model. It is found that Joule heating plays a significant role in the electro-induced phase transition of VO2. Furthermore, the ambient temperature has an obvious regulation effect on the phase transition voltage of VO2 film. The research results can provide efficient guidance to the preparation of VO2 film and the application and regulation of electro-induced phase transition.

In this study, we propose a novel method to determine the vitamin C content in fruits and vegetables. The proposed method exploits the image and data processing abilities of computers by coupling a digital camera and a color reaction. An image acquisition device was developed to collect the image information of the solution to be measured after the color reaction. The corresponding RGB and Lab color components were obtained by an image analysis software. Further, the standard curves of the vitamin C concentration and color component were established by nonlinear, linear, and multivariate data fitting. The detection range was 0.81-20.00 µg mL-1 (R2 = 0.9994), LOD was 0.24 µg mL-1, LOQ was 0.81 µg mL-1, accuracy was 98.95%, and precision was determined with an RSD of 0.73%. A comparison of the results confirmed that the proposed method’s accuracy was higher than that of the spectrophotometric method. The proposed method has a simple design and facilitates easy operation, and the cost of the equipment is only US$ 31.43. Therefore, it can replace the traditional spectrophotometric method for the determination of vitamin C content in fruits and vegetables and is highly applicable in the food, chemical, and medical fields.

This study explored the reduction of adenosine triphosphate (ATP) levels in L-02 hepatocytes by hexavalent chromium (Cr(VI)) using chi-square analysis. Cells were treated with 2, 4, 8, 16, or 32 μM Cr(VI) for 12, 24, or 36 h. Methyl thiazolyl tetrazolium (MTT) experiments and measurements of intracellular ATP levels were performed by spectrophotometry or bioluminescence assays following Cr(VI) treatment. The chi-square test was used to determine the difference between cell survival rate and ATP levels. For the chi-square analysis, the results of the MTT or ATP experiments were transformed into a relative ratio with respect to the control (%). The relative ATP levels increased at 12 h, decreased at 24 h, and increased slightly again at 36 h following 4, 8, 16, 32 μM Cr(VI) treatment, corresponding to a "V-shaped" curve. Furthermore, the results of the chi-square analysis demonstrated a significant difference of the ATP level in the 32-μM Cr(VI) group (P < 0.05). The results suggest that the chi-square test can be applied to analyze the interference effects of Cr(VI) on ATP levels in L-02 hepatocytes. The decreased ATP levels at 24 h indicated disruption of mitochondrial energy metabolism and the slight increase of ATP levels at 36 h indicated partial recovery of mitochondrial function or activated glycolysis in L-02 hepatocytes.