浅析教学中的关联速度问题

高中物理学习过程中,在学习运动的合成与分解时,教师和学生都会遇到一些经典的关联速度问题.学生解决此类问题时也常常出错,教师的讲解往往看似合理,实质还是有背逻辑思维.文章分析了关联速度中的经典例题:绳拉船的问题,并且指出了许多教师的解法存在的争议,还讨论了更合理的常规解法和适于中学生理解的方法.文章中的"关联速度问题的中...     

Flavonoids from Lycium barbarum Leaves Exhibit Anti-Aging Effects through the Redox-Modulation

Lycium barbarum leaves are a kind of vegetable, and modern nutrition studies have found that they have an anti-aging function. Our study aims to investigate the anti-aging effects of Lycium barbarum leaf flavonoid (LBLF) extracts and its underlying molecular mechanism. LBLFs were purified using D101 and polyamide resin, characterized by ultraperformance liquid chromatography coupled with mass spectrometry, and administered to hydrogen peroxide (H₂O₂)-treated human umbilical vein endothelial cells (HUVECs) and Caenorhabditis elegans. Appropriate enrichment conditions were optimized through dynamic adsorption and desorption experiments, the content of flavonoids reached 909.84 mg/g, rutin and kaempferol being the main ones. LBLFs attenuated H₂O₂-induced HUVEC apoptosis, decreased reactive oxygen species and malondialdehyde production levels, increased superoxide dismutase, glutathione peroxidase and catalase activities. Furthermore, pre-treatment with LBLF increased mRNA expression of erythropoietin (EPO) and heme oxygenase-1 (HO-1) via the mitogen-activated protein kinase (MAPK) signaling pathway in HUVECs. Compared with 100 µM rutin monomer, LBLF prolonged the lifespan of Caenorhabditis elegans, enhanced their mobility in middle life stages and upregulated expression of sod-2, gcs-1 and skn-1 genes, which indicated that the anti-aging effects of LBLF were due to its redox-modulation.     

一种高性能太阳敏感器复合光学系统设计

以夫朗禾费衍射理论为基础,结合微透镜,设计了一种高性能的数字式太阳敏感器复合光学系统。分析了光学系统的组成,建立了光学系统的数学模型,设计了光学系统的焦距、孔径和微透镜参量,并进行了成像的数值仿真。仿真结果表明,与基于掩模的光学系统相比,这种新型的复合光学系统成像光斑能量分布集中,保证计算光斑中心位置的高精度,使敏感器具有大视场和高精度的特点。     

大孔高镍LiNi0.8Co0.1Mn0.1O2正极材料的制备及其电化学性能研究

本工作以聚甲基丙烯酸甲酯(PMMA)微球组装成的胶晶模板作为铸模,溶胶-凝胶法辅助获得大孔LiNi0.8Co0.1Mn0.1O2 (NCM811)正极材料.结果 表明,利用PMMA作为造孔剂,形成了由100nm的颗粒堆积而成的大孔结构,这种结构有效地提高了材料的倍率性能和循环稳定性.大孔NCM811在0.1C的首次放电...     

Chemical Constituents from the Flowers of Carthamus tinctorius L. and Their Lung Protective Activity

A new flavonoid, saffloflavanside (1), a new sesquiterpene, safflomegastigside (2), and a new amide, saffloamide (3), together with twenty-two known compounds (4–25), were isolated from the flowers of Carthamus tinctorius L. Their structures were determined based on interpretation of their spectroscopic data and comparison with those reported in the literature. The protective effects against lipopolysaccharide (LPS)-stimulated damage on human normal lung epithelial (BEAS-2B) cells of the compounds were evaluated using MTT assay and cellular immunofluorescence assay. The results showed that compounds 2–3, 8–11, and 15–19 exhibited protective effects against LPS-induced damage to BEAS-2B cells. Moreover, compounds 2–3, 8–11, and 15–19 can significantly downregulate the level of nuclear translocation of NF-κB p-p65. In summary, this study revealed chemical constituents with lung protective activity from C. tinctorius, which may be developed as a drug for the treatment of lung injury.     

Facile Synthesis of Porous Ag Crystals as SERS Sensor for Detection of Five Methamphetamine Analogs

Porous noble metal nanomaterials have attracted extensive attention due to their high specific surface area and surface plasmon resonance effect. However, it is difficult to form porous structures due to the high mobility and low reduction potential of noble metal precursors. In this article, we developed a facile method for preparing porous Ag with a controllable structure at room temperature. Two kinds of Ag crystals with different porous structures were successfully prepared by using AgCl cubes as sacrificial templates. Through the galvanic replacement reaction of Zn and AgCl, Ag crystals with a sponge-like porous structure were successfully prepared. Additionally, using NaBH₄ as the reducing agent, we prepared granular porous Ag cubes by optimizing the amount of reducing agent. Both the sponge-like and granular porous Ag cubes have clean and accessible surfaces. In addition, we used the prepared two porous Ag cubes as substrate materials for SERS detection of five kinds of methamphetamine analogs. The experimental results show that the enhancement effect of granular porous Ag is better than that of sponge-like porous Ag. Furthermore, we probed the hot spot distribution of granular porous Ag by Raman mapping. By using granular porous Ag as the substrate material, we have achieved trace detection of 5 kinds of methamphetamine analogs including Ephedrine, Amphetamine, N-Methyl-1-(benzofuran-5-yl)propan-2-amine (5-MAPB), N-Methyl-1-(4-methoxyphenyl)propan-2-amine (PMMA) and N-Methyl-1-(4-fluorophenyl)propan-2-amine (4-FMA). Furthermore, to achieve qualitative differentiation of analogs with similar structures we performed density functional theoretical (DFT) calculations on the Raman spectra of the above analogs. The DFT calculations provided the vibrational frequencies, Raman activities, and normal mode assignment for each analog, enabling the qualitative differentiation of the above analogs.     

Effect of Thermal Processing on the Metabolic Components of Black Beans on Ultra-High-Performance Liquid Chromatography Coupled with High-Field Quadrupole-Orbitrap High-Resolution Mass Spectrometry

An ultra-high-performance liquid chromatography coupled with high-field quadrupole-orbitrap mass spectrometry (UHPLC-QE-MS) histological platform was used to analyze the effects of two thermal processing methods (cooking and steaming) on the nutritional metabolic components of black beans. Black beans had the most amino acids, followed by lipids and polyphenols, and more sugars. Multivariate statistical analysis indicated that heat processing significantly affected the metabolic component content in black beans, with effects varying among different components. Polyphenols, especially flavonoids and isoflavones, were highly susceptible. A total of 197 and 210 differential metabolites were identified in both raw black beans and cooked and steamed black beans, respectively. Cooking reduced the cumulative content of amino acids, lipids, polyphenols, sugars, and nucleosides, whereas steaming reduced amino acid and lipid content, slightly increased polyphenol content, and significantly increased sugar and nucleoside content. Our results indicated that metabolic components were better retained during steaming than cooking. Heat treatment had the greatest impact on amino acids, followed by polyphenols, fatty acids, sugars, and vitamins, indicating that cooking promotes the transformation of most substances and the synthesis of a few. The results of this study provide a basis for further research and development of nutritional products using black beans.     

A MXene-derived redox homeostasis regulator perturbs the Nrf2 antioxidant program for reinforced sonodynamic therapy

Ultrasound (US)-mediated sonodynamic therapy (SDT) has emerged as a spatiotemporally controllable therapeutic modality in combating cancer because of its high tissue-penetration depth and minimal invasiveness. However, the elevated nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant program in cancer cells can serve as a chief reactive oxygen species (ROS) detoxification system to alleviate oxidative injury and promote tumorigenesis, and thus greatly antagonize the therapeutic efficacy of ROS-mediated anticancer therapies. Herein, we report that vanadium carbide MXene-derived carbon dots (PMQDs) can act as high-efficacy sonosensitizers to efficiently generate ROS upon US irradiation and simultaneously hinder the Nrf2 antioxidant program for enhanced sonodynamic therapy of cancer. These PMQDs show superior US-triggered ROS generating ability because of their efficient migration/separation of electron–hole pairs and narrow bandgap. Importantly, these PMQDs can serve as efficient redox homeostasis regulators to perturb the Nrf2 antioxidant mechanism and thus reduce its effects on ROS neutralization for enhanced SDT efficacy. Overall, the present study will not only provide a new paradigm to augment SDT by perturbing the Nrf2 antioxidant program, but also give valuable insights into developing high-efficacy MXene-derived nanoagents for cancer therapy.

A redox homeostasis regulator has been developed as a high-efficacy sonosensitizer to efficiently generate reactive oxygen species upon ultrasound irradiation and simultaneously hinder the Nrf2 antioxidant program for enhanced sonodynamic therapy.     

气相生长氮化铝单晶的新方法

通过在钨坩埚盖开小孔的方法改变氮化铝结晶衬底上的温度场分布,在开孔处形成局部低温区;由于孔的几何尺寸的限制和氮化铝晶体生长的各向异性,开孔处的氮化铝晶体单晶化;随后,开孔处的单晶起籽晶的作用,逐渐长成较大尺寸、较高质量的氮化铝单晶.目前用该方法已经制备出直径大于2mm的氮化铝单晶体.     

神府煤焦与水蒸气、CO2气化反应特性研究

采用高温微量热天平和自制水蒸气发生装置进行神府煤焦与水蒸气和CO2气化实验,考察热解速率、不同气化剂(CO2和水蒸气)以及温度对气化反应的影响.用扫描电镜和吸附仪测定煤焦的初始结构.两种煤焦孔径为2 nm～170 nm的孔占总孔容的90%以上.神府快速煤焦(FP)与水蒸气气化活性比慢速煤焦(SP)高4.16倍,FP比SP挥发分脱除快,破坏其孔结构,减少缔合机会和二次反应.SP的BET比表面积为1.077 7 m2/g,FP的BET比表面积为1.893 9 m2/g.SP与水蒸气气化活性是CO2的9.94倍,FP与水蒸气的气化活性是CO2的7.15倍,水蒸气比CO2气化时进入的孔径范围广及水蒸气比CO2更容易解离.同种煤焦与水蒸气和CO2气化时的气化速率与转化率之间的趋势相近.用随机孔模型拟合并求取反应动力学参数,温度对SP与水蒸气、CO2反应速率,以及FP与水蒸气反应速率影响相似,而对FP与CO2反应速率影响明显比前三个反应要小.