共查询到20条相似文献,搜索用时 0 毫秒
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Abstract A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000°C in a continuous stream of helium and oxygen. CO2 removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO2 is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1‰. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOC) of groundwater from Germany yielded consistent values of δ13C = -28.8‰. 相似文献
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Optics and Spectroscopy - The laser-induced emission of carbon materials is studied experimentally. We observed broadband emission spectra in the visible region, as well as a red shift of the... 相似文献
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We calculate the dependence of the signal-to-noise ratio and gain on the angle α between the pump and signal beams and the beam ratio β in Cu-doped potassium-sodium-strontium-barium niobate (Cu:KNSBN) crystal and compare them with the experimental results available in the literature. We find good qualitative agreement between the calculated and experimental results. Also we study variations of SNR and gain with α and β in BaTiO3 crystal. Experimental data for this crystal are not available. 相似文献
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Zieliński M Zielińska A Papiernik-Zielińska H Ogrinc N Kobal I 《Isotopes in environmental and health studies》2001,37(3):239-252
13C kinetic isotope effect (KIE) in the decarboxylation of phenylpropiolic acid (PPA) in tetralin medium (Tn) has been determined at 409-432 K and found to be of magnitude similar to the 13C KIE observed in the decarboxylation of malonic acid where the rupture of the C-C bond is the rate determining step. 13C KIE equals 1.0318/at 136 degrees C in the decarboxylation of PPA in Tn medium. Intramolecular 13C KIE in the decarboxylation of malonic acid equals 1.0316 at this temperature. Thus it has been shown that the nearly "full" 13C KIE can be achieved by providing the excess hydrogen to Calpha of PPA (or to triple acetylene bond) using not only strong mineral acids as the source of protons but also by carrying out the decarboxylation in organic medium like tetralin. A mechanism of decarboxylation of PPA in Tn is suggested. 相似文献
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用紫外分光光度法,找出介孔碳材料对蛋白质的最佳吸附条件,并测定出该介孔碳材料对溶菌酶的最大吸附量.主要从3方面研究介孔碳材料对蛋白质吸附行为的影响.分别是介孔碳材料对蛋白质吸附行为随接触时间的变化产生的影响,pH值的改变对介孔碳材料吸附蛋白质行为的影响,以及介孔碳材料的量的改变对蛋白质吸附行为随接触时间的变化产生的影响.结果表明,当溶菌酶溶液的初始浓度为210μmol/L,pH值为11.0,接触时间为96h时介孔碳材料对蛋白质即可达到吸附饱和.该介孔碳材料在最佳条件下对溶菌酶的最大吸附量为27.32μmol/g,表现出优越的溶菌酶吸附性能. 相似文献
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悬浮液氢化物发生原子荧光光谱法测定化探样品中痕量铋 总被引:10,自引:0,他引:10
本文提出了一种把悬浮液技术与氢化物发生法相结合原子荧光光谱测定化探样品中痕量铋的分析方法,试验了悬浮粒度,酸介质,悬浮液浓度等因素对铋氢化物发生效率的影响,采用水溶液标准校正,方法简便,结果准确可靠。 相似文献
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为克服光催化材料可见光利用效率低的缺陷, 通过三聚氰胺高温缩聚的方法合成了石墨型氮化碳(g-C3N4)材料。采用XRD, SEM, UV-Vis技术对氮化碳材料的微观结构和光学性能进行了表征, 并通过降解罗丹明B溶液研究了缩聚温度和不同光源对光催化效率的影响。结果表明, 合成的氮化碳层片状结构保存良好, 尽管材料表面在高温下断裂形成了不规则的块体颗粒;随着煅烧温度的升高, 催化剂在紫外光和可见光部分的吸收都显著增强, 这可能是由于材料表面的岩石状块体颗粒提高了材料的比表面积, 同时降低了光的反射又提高了对光的吸收。在罗丹明B的光降解测试中, 催化剂在可见光和太阳光照射下均表现出了良好的催化效果, 缩聚温度为580 ℃时效果最好, 分别为94.8%(60 min)和91.1%(90 min)。该方法制备的石墨型氮化碳催化剂对利用清洁能源进行环境净化应用具有极大的潜在价值。 相似文献
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Christian T. Herbst 《Journal of voice》2021,35(3):365-375
Subharmonics are an important class of voice signals, relevant for speech, pathological voice, singing, and animal bioacoustics. They arise from special cases of amplitude (AM) or frequency modulation (FM) of the time-domain signal. Surprisingly, to date there is only one open source subharmonics detector available to the scientific community: Sun’s subharmonic-to-harmonic ratio (SHR). Here, this algorithm was subjected to a formal evaluation with two data sets of synthesized and empirical speech samples. Both data sets consisted of electroglottographic (EGG) signals, ie, a physiological correlate of vocal fold oscillation that bypasses vocal tract acoustics. Data Set I contained 2560 synthesized EGG signals with varying degrees of AM and FM, fundamental frequency (fo), periodicity, and signal-to-noise ratio (SNR). Data Set II was made up of 25 EGG samples extracted from the CMU Arctic speech data base. For a “ground truth” of subharmonicity, these samples were manually annotated by a group of five external experts. Analysis of the synthesized data suggested that the SHR metric is relatively robust as long as the subharmonic modulation extent is below 0.35 and 0.7 for the FM and AM scenarios, respectively. In the CMU Arctic speech data samples, the SHR analysis reached a maximum sensitivity of about 87% at a specificity of over 90%, but only for adaptive algorithm parameter settings. In contrast, the algorithm’s default parameter settings could only successfully classify about 9% of all subharmonic instances. The SHR is a useful metric for assessing the degree of subharmonics contained in voice signals, but only at adaptive parameter settings. In particular, the frequency ceiling should be set to five times the highest fo, and the frame length to at least five times the largest fundamental period of the analyzed signal. For subharmonic classification a threshold of SHR ≥ 0.01 is recommended. 相似文献
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K.J. Liu M. Miyake P.E. James H.M. Swartz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,133(2):291-298
Carbon based paramagnetic materials are frequently used for EPR oximetry, especiallyin vivo,but the EPR spectra of these materials often have more than one paramagnetic center and/or relatively low signal intensity. To determine whether the multi-components of carbon based materials could be separated and enriched in the active component, we used density gradient centrifugation to separate the materials into several fractions. We studied two types of coals, gloxy and Pocahontas, and found these materials to have large density distribution. The separated density fractions had very different EPR spectra and intensities. The active component from the coal material had a more homogeneous EPR signal and significantly increased EPR signal intensity, whereas for India ink, only slight changes were observed. This result can be very useful in the development of better probes for EPR oximetry. 相似文献
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The 0.79 eV photoluminescence spectrum known to emerge in oxygen-rich irradiated silicon is studied in 13C and 18O enriched crystals. The principal no-phonon transition at 0.79 eV splits into a doublet in the 13C enriched sample in a way directly demonstrating that one carbon atom per center is optically active. In contrast, no isotope effects are observed in the local mode replicas. Doping the silicon with 18O slightly influences two local mode replicas giving the first direct evidence that oxygen is involved in the defect. 相似文献
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Kristina L. Hitzfeld Hans-Hermann Richnow 《Isotopes in environmental and health studies》2017,53(2):116-133
In this study conversion conditions for oxygen gas chromatography high temperature conversion (HTC) isotope ratio mass spectrometry (IRMS) are characterised using qualitative mass spectrometry (IonTrap). It is shown that physical and chemical properties of a given reactor design impact HTC and thus the ability to accurately measure oxygen isotope ratios. Commercially available and custom-built tube-in-tube reactors were used to elucidate (i) by-product formation (carbon dioxide, water, small organic molecules), (ii) 2nd sources of oxygen (leakage, metal oxides, ceramic material), and (iii) required reactor conditions (conditioning, reduction, stability). The suitability of the available HTC approach for compound-specific isotope analysis of oxygen in volatile organic molecules like methyl tert-butyl ether is assessed. Main problems impeding accurate analysis are non-quantitative HTC and significant carbon dioxide by-product formation. An evaluation strategy combining mass spectrometric analysis of HTC products and IRMS 18O/16O monitoring for future method development is proposed. 相似文献
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Interactions of plasma with the walls lead to particle release by various mechanisms and the amount of impurities in the plasma core limits the performance of the device. It is very important to get the particle fluxes for understanding the releasing mechanisms of impurities. The spectroscopic measurements to determine the impurity influx from localized surfaces in tokamak plasma is described in detail in Ref. Determined the origin of the chromium influxes by this method in ASDEX during ICRF heating were reported in Ref. 相似文献
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利用多孔碳实现SO2脱除和高值资源化具有耗水少、吸附剂可循环等优点,是当前重要技术方向,探究SO2在碳材料纳米空间中的吸附转化机制是该技术的理论基础。前期研究表明O2存在的条件下,碳材料中SO2会被催化氧化形成SO3,但具体的吸附催化位点和氧化路径有待进一步研究。本文采用密度泛函理论计算了SO2碳材料锯齿形不饱和碳原子处的吸附和催化氧化路径,发现:SO2和O2在不饱和碳原子处发生化学吸附。当O2在不饱和碳原子处优先吸附时,SO2会与活化的O2反应生成SO3和化学吸附态的O;当SO2在不饱和碳原子处优先吸附时,O2会在S原子附近活化,活化后的O2会与SO2反应生成气相SO3、化学吸附态SO3。本文计算结果为用于硫资源化的高性能碳材料合成提供了理论指导。 相似文献
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Abstract The Carbon Rod Atomizer (CRA) was evaluated for routine trace analysis of vanadium in crude oil by atomic absorption spectroscopy with a carbon (graphite) tube as a micro-furnace. Two crude oil samples were analyzed, both by standard addition and standard working curve methods, and the results confirmed by analysis with flame atomic absorption spectroscopy using a fuel-rich nitrous oxide-acetylene flame. Because of the relative involatility of vanadium at the temperature of the CRA, quantitative recoveries of vanadium in crude oil occur only when the vanadium content of the sample injected into the CRA does not exceed the limit of about 1 × 10?8 g. A sensitivity (weight/1% absorption) of 7.0 × 10?11 g and detection limit (signal-to-root-mean-square-noise equal to two) of 6.9 × 10?12 are reported. 相似文献