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81.
选择学生比较熟悉的碘元素,结合海带提碘和精碘制碘酸钾工业生产情境展开复习教学,综合利用元素性质、反应原理探索含碘物质之间相互转化的最优路径,并对转化过程中的某些现象进行实验探究。通过设置有梯度的问题串引导学生在思考、分析、探究、归纳中完成综合型学习任务,实现知识规律化和体系化整合以及高阶思维培养。  相似文献   
82.
A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.  相似文献   
83.
研究了低功率超声(US, <38 W)对NaClO氧化非离子型碘代X射线造影剂—碘帕醇(IPM)的增强作用及机理, 考察了NaClO添加浓度和超声功率的影响, 分析并计算了体系中的主要活性物种及其贡献. 采用高效液相色谱/串联质谱(HPLC/MS/MS)对降解产物进行分析, 推测IPM的降解路径. 结果表明, 低功率US显著增强了NaClO对IPM的氧化效果, 在25 ℃, pH=5.8, NaClO浓度为0.12 mmol/L条件下, 10 mg/L IPM在60 min的降解率达到85.8%. 其中NaClO氧化、 HO·和活性氯自由基(RCSs)是US/NaClO增强IPM降解的主要原因, 自由基分析计算它们的贡献率分别为15.82%, 4.65%和79.53%. NaClO浓度在0~0.24 mmol/L范围内, IPM的降解率随NaClO浓度升高而增加, 60 min后降解率由4.75%增加到91.12%; 超声功率为28.5 W, 降解率达到最高. 在 15~45 ℃温度范围内, IPM的降解过程符合表观一级反应动力学, 反应活化能(Ea)为59.03 kJ/mol. HPLC/MS/MS共检测出5种中间产物, 结合密度泛函理论(DFT)计算结果, 初步推测了IPM在US/NaClO体系中的降解途径和机理.  相似文献   
84.
采用高温固相法成功制备了Na3Sc2-x-y(PO4)3xTm3+,yDy3+荧光粉,利用X射线衍射仪、扫描电子显微镜和荧光光谱仪对荧光粉进行了物相、形貌和发光性能进行了表征。 在Na3Sc2(PO4)3∶0.06Tm3+,yDy3+荧光粉中,物质的量分数6%的Tm3+和6%的Dy3+在360 nm激发下呈现出白光发射,其发射光谱在460~685 nm范围内存在Tm3+位于457 nm的特征发射峰,对应于Tm3+3H61D2跃迁,以及Dy3+位于483、577和672 nm处的3个特征发射峰,分别对应于Dy3+4F9/26H15/24F9/26H13/24F9/26H11/2的跃迁。 观测到Na3Sc2(PO4)3∶Tm3+荧光粉的发射光谱与Na3Sc2(PO4)3∶Dy3+的激发光谱有较好的重叠,且Tm3+的荧光寿命随Dy3+浓度的增加逐渐降低,因此在Na3Sc2(PO4)3∶Tm3+,Dy3+荧光粉中存在Tm3+向Dy3+的能量传递。 利用Dexter和Reisfeld近似分析了能量转移机制,发现从Tm3+到Dy3+的能量传递临界距离为1.6 nm,能量传递过程是通过偶极-偶极相互作用进行的。 Na3Sc2(PO4)3∶0.06Tm3+,0.06Dy3+荧光粉具有较好的耐受热猝灭性能,在423、473和523 K时的发射强度分别为298 K时发射强度的97.6%、89.2%和78.6%。 随着Dy3+浓度的增加,Na3Sc2(PO4)3∶0.06Tm3+,yDy3+荧光粉的发光颜色由蓝色转变为白色,再由白色变黄色。 Na3Sc2(PO4)3∶Tm3+,Dy3+荧光粉作为一种可调色或单相白光荧光粉在发光二极管上具有潜在的应用前景。  相似文献   
85.
Xiao  Fuchuan  Gao  Jie  Huang  Xuanting  Hu  Qingjian  Li  Ran  Zhang  Xinxiang 《Cellulose (London, England)》2021,28(9):5463-5475
Cellulose - Poly(methylhydrogen)siloxane (PMHS) was applied for hydrophobic modification of bamboo flour (BF) at room temperature based on the dehydrogenation between hydroxyl groups of BF and...  相似文献   
86.
This paper summarizes a study of controlled migration of an antifog (AF) additive; sorbitan monooleate (SMO), from linear low density polyethylene (LLDPE) films containing a compatibilizer, LLDPE grafted maleic anhydride (LLDPE‐g‐MA). LLDPE/LLDPE‐g‐MA/SMO blends were prepared by melt compounding. Bulk and surface properties of compression molded LLDPE films containing SMO and LLDPE‐g‐MA were characterized using Fourier transform infrared spectroscopy and contact angle measurements. Thermal properties were investigated using a thermal gravimetric analyzer. Diffusion coefficient (D) was calculated, and AF properties were characterized using a “hot fog” test. Compression molded films were characterized for their morphology using high‐resolution scanning electron microscopy, and rheological properties were measured using a parallel‐plate rotational rheometer. It was found that the LLDPE/LLDPE‐g‐MA/SMO systems are characterized by a slower SMO migration rate, a lower diffusion coefficient, and lower contact angle values compared with LLDPE/SMO blends. These results are well correlated with results of a hot fog test. Morphological studies revealed a very fine dispersion of SMO in the LLDPE films, when 3 phr LLDPE‐g‐MA was combined with 1 phr SMO. Thermal analysis results show that the incorporation of 3 phr LLDPE‐g‐MA and 1 phr SMO significantly increases the decomposition temperature of the blend at T > 400°C. At high shear rates, the LLDPE blends show that the AF and the compatibilizer have a lubrication effect on LLDPE. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
87.
Asymmetric hydrogenation of aromatic quinolin‐3‐amines was successfully developed with up to 94 % enantiomeric excess (ee). Introduction of the phthaloyl moiety to the amino group is crucial to eliminate the inhibition effect caused by the substrate and product, to activate the aromatic ring, and to improve the diastereoselectivity. This new methodology provides direct and facile access to chiral exocyclic amines. Notably, this report is the first on the highly enantioselective hydrogenation of aromatic amines.  相似文献   
88.
A facile method for the large‐scale synthesis of SnO2 nanocrystal/graphene composites by using coarse metallic Sn particles and cheap graphite oxide (GO) as raw materials is demonstrated. This method uses simple ball milling to realize a mechanochemical reaction between Sn particles and GO. After the reaction, the initial coarse Sn particles with sizes of 3–30 μm are converted to SnO2 nanocrystals (approximately 4 nm) while GO is reduced to graphene. Composite with different grinding times (1 h 20 min, 2 h 20 min or 8 h 20 min, abbreviated to 1, 2 or 8 h below) and raw material ratios (Sn:GO, 1:2, 1:1, 2:1, w/w) are investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, field‐emission scanning electron microscopy and transmission electron microscopy. The as‐prepared SnO2/graphene composite with a grinding time of 8 h and raw material ratio of 1:1 forms micrometer‐sized architected chips composed of composite sheets, and demonstrates a high tap density of 1.53 g cm?3. By using such composites as anode material for LIBs, a high specific capacity of 891 mA h g?1 is achieved even after 50 cycles at 100 mA g?1.  相似文献   
89.
90.
Treatment of Na[Re(CO)5] with RC?CCO2Et (R=phenyl, naphthalen‐1‐yl, phenanthren‐9‐yl and pyren‐1‐yl) followed by reaction with acetyl chloride and ethanol afforded the rhenacyclobutadienes Re{‐C(R)?C(CO2Et)C(OEt)?}(CO)4. Reactions of these rhenacyclobutadienes with HC?COEt produced rhenabenzenes Re{‐C(R)?C(CO2Et)C(OEt)?CHC(OEt)?}(CO)4. Except for R=Ph, new rhenacyclobutadienes with pendant alkenyl substituents Re{‐C(R)?C(C(OEt)?CH(CO2Et))C(OEt)?}(CO)4 were also isolated from these reactions. The NMR spectroscopic and X‐ray structural data, as well as the aromatic stabilization energy (ASE) values suggest that the rhenabenzenes are aromatic, with extensive delocalized π character.  相似文献   
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