共查询到20条相似文献,搜索用时 218 毫秒
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初中物理:“水的热膨胀的特点”的演示在我数年的教学中一直没有做过,这主要是因为:当堂演示太费时间又和讲课配合不好,如让学生等着看实验结果,则大部同学感到索然无味,如不等结果而先讲其他内容,则又打乱了课堂的系统性。加以有些学校根本没有水的最大密度演示器,因之过去讲这一节时,往往只用挂图一讲了事。但后来在物理通报上看到一些老师对这个演示采取了各种不同的方法,从而取得了较好的成绩。为了提高教学质量,我把通报上前后所介绍的几种方法都做了几遍,从不断变换着的操作中给了我新的启示,我又用了 相似文献
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初中物理学上册第三章第35节大气压的一个实验是:水由喷嘴向压强较低的玻璃管中喷入(见原书图55)。这个实验如果没有抽气机,就很难做。我 相似文献
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气体的压强与体积的关系的实验设计陈银潭(江苏兴化市合塔中学225742)实验目的探索气体的压强与体积的关系.方法一实验器材50ml玻璃注射器一只,彩色橡皮膜一块(或小气球).器材装置(图1)图1实验步骤h用橡皮膜做成直径约Zem的小气球,扎紧口后放人... 相似文献
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用ReaxFF/lg反应力场模拟CL20/BTF共晶在2000~3000 K高温条件下的热分解过程,获得了势能和物种数的演化、初始反应路径及热分解产物等详细信息。通过指数函数对势能的演化曲线进行拟合得到反映特征时间等参数,采用经典的Arrhenius反应速率方程描述总包反应,获得CL20/BTF共晶的活化能Ea=60.8 kcal/mol。研究得到CL20/BTF共晶热分解的初始路径,CL20分子中N-NO2首先断裂,在热分解起始阶段占主导作用。在不同温度条件下,CL20分子均在BTF分子前完全分解。CL20/BTF共晶的主要产物为NO2、NO、NO3、HNO、N2、H2O、CO2、O2、N2O、HONO 等。温度对产物均产生一定程度的影响. 相似文献
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Zhiyin Wang Tian-Lei Zhang Ming-Jing Li Qiong Xu Rui Wang Soumendra Roy 《Molecular physics》2018,116(13):1756-1771
CBS-QB3 method has been employed to determine the geometries, the vibrational frequencies of the reactants, the products and the transition states involved in intramolecular hydrogen-transfer and decomposition reactions of the free gas-phase H3N···HN(NO2)2 (ADN*). The results show that the intramolecular hydrogen-transfer reaction of ADN* is more feasible than that of HDN. ADN* and its hydrogen-transfer isomers ADN*-IIa,b,c decompose along four channels to form NH3 + HONO + 2NO (PI), ?H + ?O3 + N2 + NH3 (PII), ?H + ?O2 + N2O + NH3 (PIII), and HNO3 + N2O + NH3 (PIV), respectively. It has been found that the dominant decomposition channels are PI and PIII. The hydrogen-transfer reaction can reduce the barrier of elimination of NO2 and forming N2O reactions in ADN* and HDN. The decomposition of ADN*-IIc to form NO2 and N2O is more feasible than that of the gas-phase HDN. The rate constants (k) of rate-determining step of ADN* show that kPI and kPIII are higher than kPIV and kPII. Compared with HDN-IIc → N2O+?H+?O2, kPIII of ADN*-IIc is significantly higher than that of kHDN-IIc. These results reveal that NH3 (as a chaperon) has a certain influence on the decomposition mechanisms and kinetics of ADN*. 相似文献
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The infrared spectra of eighteen complexes of general formula trans-[Co(NO2) (acac)2 (R-C6H4NH2)] (acac = acetylacetonate anion, R = 3- or 4-aniline substituent) are discussed. 15N-Labelling of the complexes containing aniline and p-toluidine yields assignments of the N-H, C-N and Co-N stretching frequencies and the N-H bending frequencies. These assignments receive support from the observed frequency shifts induced by varying the substituent R which also permits the assignment of the Co-o stretching frequencies. 相似文献
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D. Koppisch E.-D. Schulze G. Gebauer 《Isotopes in environmental and health studies》2013,49(1-2):77-84
Abstract Calamagrostis villosa dominates the understory vegetation in declining spruce forests at higher elevations of the Central European mountain areas which show symptoms of needle yellowing and associated magnesium (Mg) deficiency. It was hypothesized that grasses would preferentially take up nitrate-nitrogen (NO3-N) over ammonium-nitrogen (NH4-N) which would support the cation balance in Mg deficient soils. In order to test this hypothesis, growth experiments were carried out in the greenhouse using plants which were cultivated in sand for nine weeks with full nutrient solution containing 0.2 or 2 mmol of N with different NH4 + to NO3 ? ratios (1:0, 0.5:0.5, 0:1). In a short term experiment with labelled 15NH4 + and 15NO3 ?, uptake of NH4 + and NO3 ? was measured. When NO3 ? was the only N source it was taken up at similar rate per g dry mass as in the experiment in which NH4 + was the only N source. However, at high supply pure NO3 ? nutrition resulted in higher biomass. In contrast, supply of only NH4 + caused accumulation of N in the roots but growth remained restricted. If NH4 + and NO3 ? were supplied at equal amounts, NH4 + was the preferred form for N uptake. Biomass of the plants with mixed supply did not differ from the plants with pure NO3 ? nutrition. The results point to an interesting interaction of carbon and nitrogen relation, but they do not support the initial hypothesis that grasses may prefer NO3 ? over NH4 +. 相似文献
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Selective catalytic reduction (SCR) of NOx is one of the important strategies in regulating NOx emissions. In the past several decades, the reactions of NOx (mainly NO) with H2, CO, NH3 and hydrocarbons have been extensively investigated under ambient conditions and have been summarized in numerous reviews. Nonetheless, many questions appear to be difficult to answer under ambient conditions, e.g., the pathways through which the reactions proceed. The introduction and development of modern surface science technology has played an indispensable role and is widely employed in the studies of the SCR of NOx, greatly helping to elucidate the mechanisms of the reactions with CO, H2, and NH3. However, so far, there are few review papers systematically summarizing the progress of such studies.Recently, systematic surface science studies have been conducted on the mechanisms of SCR of NO with organic molecules including ethylene, benzene, and ethanol, which are much more complicated than those with H2, CO and NH3 and have drawn much less attention before. It is confirmed that these reactions can be reliably and most importantly, reproducibly probed by surface science technology, but a great deal of work remains to be done.Since Delmon et al. have provided a very thorough review of the researches on catalytic removal of NO (reactions with H2, CO and NH3) up to 1998, in which the reactions conducted both under ambient and UHV conditions were included, this review mainly concentrates on the progress made since 1998. 相似文献
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《Proceedings of the Combustion Institute》2023,39(4):4377-4385
Deep insights into the combustion kinetics of ammonia (NH3) can facilitate its application as a promising carbon-free fuel. Due to the low reactivity of NH3, experimental data of NH3 combustion can only be obtained within a limited range. In this work, nitrous oxide (N2O) and hydrogen (H2) were used as additives to investigate NH3 auto-ignition in a rapid compression machine (RCM). Ignition delay times for NH3, NH3/N2O blends, and NH3/H2 blends were measured at 30 bar, temperatures from 950 to 1437 K. The addition of N2O and H2 ranged from 0 to 50% and 0 to 25% of NH3 mole fraction, respectively. Time-resolved species profiles were recorded during the auto-ignition process using a fast sampling system combined with a gas chromatograph (GC). An NH3 combustion model was developed, in which the rate constants of key reactions were constrained by current experimental data. The addition of N2O affected the ignition of NH3 primarily through the decomposition of N2O (N2O (+M) = N2 + O (+M), R1) and direct reaction between N2O and NH2 (N2H2 + NO = NH2 + N2O, R2). The rate constant of R2 was constrained effectively by experimental data of NH3/N2O mixtures. Two-stage ignition behaviors were observed for NH3/H2 mixtures, and the corresponding first-stage ignition delay times were reported for the first time. Experimental species profiles suggested the first-stage ignition resulted from the consumption of H2. The oxidation of H2 provided extra HO2 radicals, which promoted the production of OH radicals and initiated first-stage ignition. Reactions between HO2 radicals and NH3/NH2 dominated the first-ignition delay times of NH3/H2 mixtures. Moreover, the first-stage ignition led to the fast production of NO2, which acted as a key intermediate and affected the following total ignition. Consequently, the reaction NH2 + NO2 = H2NO + NO (R3) was constrained by total ignition delay times. 相似文献
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The structural, energetic and electronic properties of germanene adsorbed with small nitrogen-based molecules, including N2, NH3, NO2 and NO, have been investigated by using first-principles calculations. The results show that all nitrogen-based molecules considered bind much stronger to germanene than to graphene due to the hybridized sp2-sp3 bonding of Ge atoms. The N2, NO and NO2 molecules all act as an acceptor, while the NH3 molecule donates electrons to germanene. We also found sizable band gaps (2–158 meV) are opened at the Dirac point of germanene through N2, NH3, and NO2 adsorptions, but with only slightly destroying its Dirac cone shape. The NO2 molecule also shows a heavy p-type doping character and makes germanene to be metallic. Moreover, when adsorbed by NO molecule, the germanene can change to be a ferromagnetic half-metal with 100% spin-polarization at the Fermi level. Overall, the different adsorption behaviors of small nitrogen-based gas molecules on germanene provide a feasible way to exploit chemically modified germanene for a wide range of practical applications, such as field-effect transistors, gas sensors and spintronic devices. 相似文献
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《Proceedings of the Combustion Institute》2023,39(4):4365-4375
The interaction between ammonia (NH3) and nitric oxide (NO) at high temperatures is studied in this work using a shock tube combined with laser absorption diagnostics. The system simultaneously measured the NH3 and NO time-histories during the reaction processes of the shock-heated NH3/NO/CO/Ar mixtures (NH3:NO ≈ 0.9:1.0 and 1.4:1.0). The absorption cross-sections of NH3 near 1122.10 cm–1 and NO at 1900.52 cm–1 (characterized in this study) were used for measuring NH3 and NO time-histories with the temperature measured by two CO absorption lines. The measured NH3 and NO time-histories at 1614–1968 K and 2.4–2.8 atm were compared with predictions of seven recent kinetics models. The predictions that based on different mechanisms are very different and the measured profiles are within the range of the predictions. The Glarborg, NUI Galway Syngas-NOx, and Mathieu mechanisms give the closest predictions to the measurements. Kinetics analyses indicate that the NH3 and NO consumption rates are extremely sensitive to the rate constants and branching ratio of NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH, which are more reliably represented in the Glarborg and NUI Galway Syngas-NOx mechanisms. The performances of Glarborg mechanisms at lower initial temperatures can be apparently improved by revising the rate constants and branching ratio of NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH. These two reactions are also the primary pathways for NO reduction and NH3 is mainly consumed via NH3 + OH = NH2 + H2O and NH3 + H = NH2 + H2. Trace amounts of NO2 and N2O impurities decompose to form O radical followed by the generation of OH radical via H-abstraction reactions, which significantly affects the predictions of NH3 and NO according to kinetics analyses. 相似文献
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A proton-conducting polymer electrolyte based on starch and ammonium nitrate (NH4NO3) has been prepared through solution casting method. Ionic conductivity for the system was conducted over a wide range of
frequency between 50 Hz and 1 MHz and at temperatures between 303 K and 373 K. Impedance analysis shows that sample with 25 wt.%
NH4NO3 has a smaller bulk resistance (R
b) compared to that of the pure sample. The amount of NH4NO3 was found to influence the proton conduction; the highest obtainable room temperature conductivity was 2.83 × 10−5 S cm−1, while at 100 °C, the conductivity in found to be 2.09 × 10−4 S cm−1. The dielectric analysis demonstrates a non-Debye behavior. Transport parameters of the samples were calculated using the
Rice and Roth model and thus shows that the increase in conductivity is due to the increase in the number of mobile ions. 相似文献