驻波热声冷却机的研究

与压缩机制冷相比,热声制冷结构简单、可靠性高和使用寿命长。本文在正常室温(20℃)和室压(1个大气压)的工作环境下以空气为声学介质来探讨热声制冷机的设计及热声制冷效果的影响因素,并制作样机进行实验研究。研究发现:板叠长度和中心位置对热声转换效率影响较大,其数值需要理论与实验相结合来确定;以空气为声学工质,在正常室温、室压下的热声制冷机,用50W的供电驱动、90 Hz工作时可实现冷热端37℃的温差。     

生物样品中亚硝酸根和硝酸根分析研究进展EI北大核心CSCD

亚硝酸根和硝酸根以盐的形式广泛存在于生活中,其测定一直是各领域的研究热点。在法医毒物分析领域,亚硝酸盐中毒案件频发,少量亚硝酸盐即可引起中毒或死亡,案件现场体内外检材中其含量测定可为案件提供证据。亚硝酸盐不稳定易氧化,小体积生物样品中亚硝酸盐和硝酸盐的测定仍是一个挑战。本文对生物样品中亚硝酸盐和硝酸盐的测定方法进行了综述,方法分为光谱法和色谱法两大类,重点综述了色谱法中准确度较高的气相色谱-质谱(GC-MS)技术,以便为2种物质的检测和相关科学研究提供参考。     

Tuning the Morphology and State of Aggregation of Fullerene C60 using Non-ionic Surfactants

Colloid Journal - The effect of various surfactants on aggregation of fullerene C60 is discussed. Formation of ordered structures via C60-surfactant interactions at a specific [C60]/[Triton X-100]...     

Electron paramagnetic resonance, optical absorption, IR and Raman spectral studies on pelecypod shell

Pelecypod shell originated from Kolleru lake of Andhra Pradesh is used in the present work. It contains Mn(II) and Fe(III) in traces. The EPR spectrum of the compound is due to Mn(II) which is in three independent sites. The three g values are evaluated with slight differences. The hyperfine component varies from 9.33 to 9.49mT. The zero field splitting parameter is also ranges from 43.8(1) to 44.1(1)mT. Using the covalence parameter the number of ligands around metal is estimated as 20. In EPR spectrum Fe(III) is identified. The optical absorption spectrum is attributed to Mn(II) in octahedral geometry. Further 10 Dq band is attributed to Fe(II) in the optical absorption spectrum. NIR spectral results are due to water fundamentals, whereas IR and Raman spectrum is due to carbonate ion fundamentals.     

蔬菜中残留农药的石墨化碳黑净化和气相色谱-质谱检测方法

研究石墨化碳黑对不同类型农药的吸附规律和对色素的吸附能力,比较了不同洗脱溶剂对色素的洗脱能力和对待测物在GCB上洗脱顺序的影响。同时测试了GCB和活性炭的吸附-解吸附等温线,表明不同的表面结构造成了两种吸附剂不同的吸附机理及对色素吸附能力的显著差别。结果表明,GCB对含有芳香环、结构具有一定对称性的农药吸附力最强,而对叶绿素吸附强于叶黄素和番茄红素。最后根据实验结果针对性地建立了残留在蔬菜中农药多残留方法:样品经GCB净化,以丙酮/乙酸乙酯(1∶1,V/V)为洗脱液,最后用气相色谱-质谱选择离子存储(GC-MS/SIS)检测,所有农药的检出限保持在0.002~0.10 mg/kg范围内。     

Determination of antibiotics in aquatic environment by solid-phase extraction followed by liquid chromatography-electrospray ionization mass spectrometry

A robust and sensitive solid-phase extraction followed by liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method for determination of antibiotics viz., fluoroquinolones, sulfamethoxazole, trimethoprim and cephalosporines in surface waters was developed. The sample recoveries on Oasis HLB cartridges were found to be >80%. Identification was carried out by LC-ESI-MS/MS. The positive ion ESI mass spectra containing the peaks of quasimolecular ions [M+H](+) allowed the determination of molecular masses whereas the fragment ions obtained by MS/MS of [M+H](+) ions permitted the structural assignment. Quantification was carried out by selective ion monitoring (SIM) using the quasimolecular ions [M+H](+) of the parent compounds. The detection and quantification limits were found to be in the range of 0.6-8.1 and 2.0-24.0 microg/L. The surface waters of different lakes and tanks of Hyderabad, India were found to contain a few antibiotics.     

Kinetics and mechanism of oxidation of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) by vanadium(V), periodate and iodate ions in acetate buffers

The kinetics of oxidation of bis(2,4,6-tripyridyl 1,3,5-s-triazine)iron(II) by vanadium(V), periodate and iodate has been studied in acetate buffers by stopped-flow and spectrophotometric methods. The oxidation reaction of bis(2,4,6-tripyridyl 1,3,5-s-triazine)iron(II) by vanadium(V), periodate and iodate follows first order kinetics for the substrate and oxidant. Hydrogen ion has no significant effect on the rate. A generalized mechanism was proposed for these reactions and these reactions follow the rate law: Rate = k [oxidant] [Fe(tptz)₂ ²⁺].     

三步法合成高封端率端氨基聚乳酸

叔丁氧羰基碳酸酐((Boc)2O)和氨基丙醇反应合成叔丁氧羰基氨基丙醇(Boc-氨基丙醇),以此为引发剂在辛酸亚锡的催化下,引发L-丙交酯开环聚合合成叔丁氧羰基氨基封端聚乳酸(BocNH-PLLA),叔丁氧羰基(Boc)经三氟乙酸处理脱除后得到端氨基聚乳酸(PLLA-NH2).以PLLA-NH2为大分子引发剂,引发ω-苄氧羰基L-赖氨酸-N-羧酸酐(ω-Z-L-Lysine-NCA)开环聚合,合成聚L-乳酸-聚ω-苄氧羰基L-赖氨酸两嵌段共聚物(P(LLA-LLz)).采用红外光谱(FT-IR)、核磁共振氢谱(1H-NMR)、凝胶渗透色谱(GPC)对聚合物结构进行了表征.结果表明:PLLA-NH2端基亲核性明显提高,可引发ω-Z-L-Lysine-NCA开环聚合制备嵌段共聚物,PLLA-NH2的合成方法简便,氨基封端率高,其分子量和单体与引发剂的摩尔比具有良好的线性关系.     

Fine-Tuning Redox Properties of Heteroleptic Molybdenum Complexes through Ligand-Ligand-Cooperativity

Heteroleptic molybdenum complexes bearing 1,5-diaza-3,7-diphosphacyclooctane (P₂N₂) and non-innocent dithiolene ligands were synthesized and electrochemically characterized. The reduction potentials of the complexes were found to be fine-tuned by a synergistic effect identified by DFT calculations as ligand-ligand cooperativity via non-covalent interactions. This finding is supported by electrochemical studies combined with UV/Vis spectroscopy and temperature-dependent NMR spectroscopy. The observed behavior is reminiscent of enzymatic redox modulation using second ligand sphere effects.