Effect of addition of a non-equidiffusional reactant to an equidiffusional diffusion flame

A Burke–Schumann (flame-sheet) formulation is developed for diffusion flames between a fuel and oxidiser with Lewis numbers of unity, subject to addition to the fuel and/or oxidiser stream of a different reactant for which the Lewis number differs from unity. This formulation is applied to laminar counterflow diffusion-flame experiments, reported here, in which hydrogen was added to either methane–nitrogen mixtures or oxygen–nitrogen mixtures at normal atmospheric pressure, with both feed streams at normal room temperature. Experimental conditions were adjusted to fix selected values of the stoichiometric mixture fraction and the adiabatic flame temperature, and the strain rate was increased gradually, maintaining the momentum balance of the two streams, until extinction occurred. At the selected sets of values, the strain rate at extinction was measured as a function of the hydrogen concentration in the fuel or oxidiser stream. The ratio of the fraction of the oxidiser flux that consumes hydrogen to the fraction that consumes fuel was calculated from the new Burke–Schumann formulation, and it was found that, within experimental uncertainty, the ratio of the extinction strain rate with hydrogen addition to that without was the same at any given value of this oxygen flux ratio, irrespective of whether the hydrogen was added on the fuel or oxidiser side. This experimental result was also in close agreement with computational predictions employing detailed chemistry. These results imply that differences in detailed hydrogen concentration profiles within the reaction zone have little or no influence on the chemical kinetics of extinction when the stoichiometric mixture fraction, the adiabatic flame temperature, and the proportion of oxygen that consumes the added fuel are fixed. This same correspondence may be expected to apply for other fuels and additives.     

Interactions of gamma rays with undoped and Mn-doped sodium phosphate glasses

Ultraviolet and visible spectroscopic measurements were used to investigate prepared undoped and Mn-doped sodium phosphate glasses before and after successive gamma irradiation. The effects of both glass composition and MnO₂ content on the generation of radiation-induced defects were investigated. Undoped sodium phosphate glass shows strong UV absorption, which is attributed to the presence of trace iron impurities present in the raw materials. Mn-doped glasses reveal an additional visible broad band centered at about 500 nm due to Mn³⁺, which has recently been related to the ⁵E_g →⁵T_2g transition. The radiation-induced bands are correlated with the generation of liberated electron–hole pairs during the process of gamma irradiation and the possibility of photochemical reactions especially with trace iron impurities and manganese ions. The intensity and the position of the induced bands are observed to depend on the type and composition of glass, concentration of the dopant and also on the irradiation dose. Manganese ions when present in relatively higher content have been found to show a shielding behavior towards the effects of progressive gamma irradiation causing a retardation of the growth of the induced defects. Infrared and Raman spectra of the undoped and Mn-doped glasses were measured to investigate the structural phosphate groups present and the effect of MnO₂ on the network structure. An ESR investigation was carried out to confirm the state of manganese ions in the prepared sodium phosphate glasses.     

Vibrational Spectroscopic and Theoretical Studies of Urea Derivatives with Biochemical Interest: N,N′-Dimethylurea,N,N,N′,N′-Tetramethylurea,and N,N′-Dimethylpropyleneurea

Abstract

Mid-infrared, far-infrared, and Raman vibrational spectroscopic studies were combined with density functional theory (DFT) calculations and normal coordinate force field analyses for N,N′-dimethylurea (DMU), N,N,N′,N′-tetramethylurea (TMU), and N,N′-dimethylpropyleneurea (DMPU: IUPAC name 1,3-dimethyltetrahydropyrimidin-2(1H)-one). The equilibrium molecular geometry of DMU (all three conformers), TMU, and DMPU and the frequencies, intensities, and depolarization ratios of their fundamental infrared (IR) and Raman vibrational transitions were obtained by DFT calculations. The vibrational spectra were fully analyzed by normal coordinate methods as well. A starting force field for DMPU was obtained by adapting corresponding force constants for DMU and TMU, resulting after refinements in the stretching force constants C=O (7.69, 7.30, 7.68 N·cm^?1), C–N (5.16, 5.55, 5.05 N·cm^?1), and C-Me (5.93, 4.00, 4.22 N·cm^?1) for DMU, TMU, and DMPU, respectively. The dominating conformer of liquid DMU was identified as trans-trans, strong intermolecular hydrogen bonding was verified in solid DMU, and weak dipole–dipole association was found in liquid TMU and in DMPU. Special attention was paid to analyzing the methyl group frequencies, which revealed deviations from local C_3v symmetry. A linear correlation was found between the CH stretching force constants and the inverse of the CH bond lengths (1/r ²). The averaged NH stretching frequencies of gaseous, dissolved, and solid urea and of DMU, with variations for hydrogen bonding of different strength, are linearly correlated to the NH stretching force constants. Characteristic skeletal vibrations were assigned for a broad variety of urea derivatives and also for pyrimidine derivatives, which all contain the N₂C=O entity. The very strong IR bands of C=O stretching (1,676 ± 40 cm^?1) and asymmetric CN₂ stretching (1,478 ± 60 cm^?1), and the very intense Raman feature of symmetric CN₂ stretching or ring breathing (757 ± 80 cm^?1), can be recognized as fingerprint bands also for the pyrimidine derivatives cytosine, thymine, and uracil, which all are nucleobases in DNA and RNA nucleotides.     

Secondary Ion Mass Spectrometry Imaging

Secondary ion mass spectrometry (SIMS) is a chemical analysis technique that employs mass spectrometry to analyze solid and low volatility liquid samples [1]. Although there are numerous configurations of SIMS instrumentation, the fundamental basis of SIMS analyses is the measurement of the mass and intensity of secondary ions produced in a vacuum by sputtering the surface of the sample with energetic ion or neutral beams. The sputtering beam is referred to as the primary beam and typically has a kinetic energy of several thousand electronvolts (keV). The primary beam removes atomic or molecular layers at a rate determined principally by the intensity, mass, and energy of the primary species and the chemical and physical characteristics of the sample [2]. Particle sputtering at the kiloelectronvolt level produces a variety of products including electrons, photons, atoms, atomic clusters, intact molecules, and distinctive molecular fragments. A small fraction of these sputter products are ionized, and these ions are the secondary ions in secondary ion mass spectrometry.     

Observation of thermoluminescence induced by fission fragments

Abstract

Thermoluminescence induced in CaF₂ powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 10¹⁰ and 6.5 × 10¹¹ n/cm² has been obtained, thus establishing the feasibility of the use of this method for fast-neutron dosimetry. A limitation of the method is that, if the fissile foil is not separated from the phosphor after irradiation, the TL produced by the α-disintegration of ²³⁸U may eventually mask the fission-induced TL.     

某工程地基基坑支护探讨

软土地基中的支护是基础工程的关键,在节约成本的前提下,选择合理的支护结构至关重要．通过对某公司将要开发的2个基坑支护方案的项目进行的相关分析、计算和探讨,总结出了软土地基中的基坑支护方案的选择原则及其相对应的施工措施等．     

靶丸支撑膜对ICF内爆性能影响的模拟研究

使用二维多群辐射扩散流体力学程序LARED-S,模拟研究靶丸支撑膜在惯性约束聚变氘氘（DD）气体靶内爆过程中的扰动演化过程及其对内爆性能的影响.二维模拟表明：靶丸支撑膜显著降低DD气体靶内爆的中子产额,二维模拟产额为一维结果的55.2%.内爆性能下降的主要物理机制是支撑膜使靶壳生成大幅度的尖钉深入DD气体区,使烧蚀层与DD气体之间物质界面处的电子热传导漏失功率显著增大,导致DD核反应速率显著降低,中子反应速率峰值时刻（bang-time时刻）提前.相比一维理想内爆的模拟结果,支撑膜引入的扰动显著降低bang-time时刻DD气体压强与内爆动能转化为DD气体内能的效率,壳层剩余动能相应大幅增加.     

Bose-Einstein condensation in spin-polarized atomic hydrogen: A new superfluid

We find that in the spin-polarized hydrogen, Bose condensation occurs for certain quantized values of the magnetic field. Once the field is fixed, sweeping of the radio-frequency results in nuclear magnetic resonance so that condensation and NMR occur simultaneously. We have found that nuclear self-induced transparency occurs. A new excitation designated by the present author as superboojum, which is a discontinuity in the hydrodynamic equations in spin-polarized hydrogen having finite nuclear as well as electronic spin is discovered.     

Pd及其含量对Au/CeO_2催化剂甲醇部分氧化制氢性能的影响

采用聚乙烯吡咯烷酮(PVP)保护乙醇还原法制备了不同Pd含量的Au-Pd/CeO2催化剂,考察了Pd及其含量对Au/CeO2催化剂甲醇部分氧化制氢反应性能的影响,并运用XRD、TPR、CH3OH-TPD和H2-TPD等技术对催化剂进行了表征。结果表明,Pd的加入提高了Au/CeO2催化剂的活性和氢气选择性,当Au/Pd     

一株嗜温高效产氢细菌Clostridium sp.08-1的分离鉴定与产氢特征

从10L连续搅拌式罐式反应器(CSTR)中分离得到1株嗜温高效产氢菌株08-1.根据菌株的形态特征和16S rDNA序列结果分析,初步鉴定菌株08-1属于Clostridium sp..同时还进一步研究了温度、pH值控制、底物浓度和种类对菌株08-1产氢的影响.结果表明.该菌株更适合利用蔗糖或成分复杂的生物质木薯粉以及废弃物厨余垃圾生长及产氢,最适产氢温度为40℃,产氢系统pH值控制在5.5时获得最大产氢量.在间歇发酵中,蔗糖浓度为20 g/L,控制温度40℃,pH值5.5,搅拌速度100 r/min时实现最大产氢速率为245 mL·(L·h)~(-1),最大产氢量达到3.06 mol.该菌株在生物制氢中具有潜在的应用价值.