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991.
A Time of flight (ToF) mass spectrometer suitable in terms of sensitivity, detector response and time resolution, for application in fast transient Temporal Analysis of Products (TAP) kinetic catalyst characterization is reported. Technical difficulties associated with such application as well as the solutions implemented in terms of adaptations of the ToF apparatus are discussed. The performance of the ToF was validated and the full linearity of the specific detector over the full dynamic range was explored in order to ensure its applicability for the TAP application. The reported TAP-ToF setup is the first system that achieves the high level of sensitivity allowing monitoring of the full 0-200 AMU range simultaneously with sub-millisecond time resolution. In this new setup, the high sensitivity allows the use of low intensity pulses ensuring that transport through the reactor occurs in the Knudsen diffusion regime and that the data can, therefore, be fully analysed using the reported theoretical TAP models and data processing. 相似文献
992.
Block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic biodegradable polyesters have been reported as thermogelling polymers, because they feature temperature-dependent sol-to-gel or gel-to-sol transitions in aqueous solutions. In this study, a series of thermogelling poly(ethylene glycol methyl ether)-block–poly(cyclohexylenedimethylene adipate)-block–poly(ethylene glycol methyl ether) triblock copolymers and PEG-block–poly(cyclohexylenedimethylene adipate) multiblock copolymers was synthesized by reacting hydroxyl-terminated poly(cyclohexylenedimethylene adipate) (PCA) with poly(ethylene glycol methyl ether) and PEG, respectively, using 1,6-diisocyanatohexane as the coupling agent. Two hydroxyl-terminated PCAs, i.e., poly(1,4-cyclohexylenedimethylene adipate) and poly(1,3/1,4-cyclohexylenedimethylene adipate), were synthesized by the condensation reaction of adipic acid (AA) with 1,4-cyclohexanedimethanol (CHDM) and 1,3/1,4-CHDM, respectively, and used as the hydrophobic polyester blocks of these thermogelling copolymers to compare the effect of crystallinity on the sol-to-gel transition behavior.The polymers were characterized using proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, solubility testing, and rheological analysis. Experimental results revealed that the structure of the PCA block (crystalline vs. amorphous), the molecular weights of the hydrophobic PCA and hydrophilic PEG blocks, and the type of thermogelling polymer (triblock vs. multiblock) influenced the solubility, polymer micelle packing characteristics, maximum storage modulus, and sol-to-gel temperature of the polymers. Among all the samples at 40 wt.% aqueous solutions, triblock copolymer TB3 showed sol-to-gel temperature at 22 °C, and had the highest maximum storage modulus about 170 Pa. 相似文献
993.
Markov models are widely used to describe stochastic dynamics. Here, we show that Markov models follow directly from the dynamical principle of maximum caliber (Max Cal). Max Cal is a method of deriving dynamical models based on maximizing the path entropy subject to dynamical constraints. We give three different cases. First, we show that if constraints (or data) are given in the form of singlet statistics (average occupation probabilities), then maximizing the caliber predicts a time-independent process that is modeled by identical, independently distributed random variables. Second, we show that if constraints are given in the form of sequential pairwise statistics, then maximizing the caliber dictates that the kinetic process will be Markovian with a uniform initial distribution. Third, if the initial distribution is known and is not uniform we show that the only process that maximizes the path entropy is still the Markov process. We give an example of how Max Cal can be used to discriminate between different dynamical models given data. 相似文献
994.
Maji S Lee JC Lu YJ Chen CL Hung MC Chen PP Yu SS Chan SI 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):3955-3968
The dioxygen activation of a series of Cu(I)Cu(I)Cu(I) complexes based on the ligands (L) 3,3'-(1,4-diazepane- 1,4-diyl)bis(1-{[2-(dimethylamino)ethyl](methyl)amino}propan-2-ol)(7-Me) or 3,3'-(1,4-diazepane-1,4-diyl)bis(1-{[2-(diethylamino)ethyl](ethyl)amino}propan-2-ol)(7-Et) forms an intermediate capable of mediating facile O-atom transfer to simple organic substrates at room temperature. To elucidate the dioxygen chemistry, we have examined the reactions of 7-Me, 7-Et, and 3,3'-(1,4-diazepane-1,4-diyl)bis[1-(4-methylpiperazin-1-yl)propan-2-ol] (7-N-Meppz) with dioxygen at -80, -55, and -35?°C in propionitrile (EtCN) by UV-visible, 77?K EPR, and X-ray absorption spectroscopy, and 7-N-Meppz and 7-Me with dioxygen at room temperature in acetonitrile (MeCN) by diode array spectrophotometry. At both -80 and -55?°C, the mixing of the starting [Cu(I)Cu(I)Cu(I)(L)](1+) complex (1) with O(2)-saturated propionitrile (EtCN) led to a bright green solution consisting of two paramagnetic species: the green dioxygen adduct [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) (2) and the blue [Cu(II)Cu(II)(μ-O)Cu(II)(L)](2+) species (3). These observations are consistent with the initial formation of [Cu(II)Cu(II)(μ-O)(2)Cu(III)(L)](1+)(4), followed by rapid abortion of this highly reactive species by intercluster electron transfer from a second molecule of complex 1 to give the blue species 3 and subsequent oxygenation of the partially oxidized [Cu(II)Cu(I)Cu(I)(L)](2+)(5) to form the green dioxygen adduct 2. Assignment of 2 to [Cu(II)Cu(II)(μ-η(2):η(2)-peroxo)Cu(II)(L)](2+) is consistent with its reactivity with water to give H(2)O(2) and the blue species 3, as well as its propensity to be photoreduced in the X-ray beam during X-ray absorption experiments at room temperature. In light of these observations, the development of an oxidation catalyst based on the tricopper system requires consideration of the following design criteria: 1)?rapid dioxygen chemistry; 2)?facile O-atom transfer from the activated cluster to substrate; and 3)?a suitable reductant to rapidly regenerate complex 1 to accomplish efficient catalytic turnover. 相似文献
995.
Siebold M Leidich P Bertini M Deflorio G Feldmann J Krupp EM Halmschlager E Woodward S 《Analytical and bioanalytical chemistry》2012,402(10):3323-3331
Element distribution in the bark of two 20-year-old clones of Picea sitchensis following wounding was studied using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Bark was sampled
at 0, 3, and 43 days after wounding and analysed using a focused Nd:YAG laser (266 nm). Intensities of 13 C, 25Mg, 27Al, 31P, 32S, 39K, 48Ca, 55Mn, 57Fe, 63Cu and 64Zn were measured by ICP-MS to study elemental distribution across the bark samples during the wound repair process. A clear
accumulation of Mg, P and K at the boundary zone between the lesion and healthy tissue was detected in the wounded samples
and was more distinctive at 43 than at 3 days after treatment. This zone of accumulation mapped onto the position of formation
of the ligno-suberised boundary zone and differentiation of the wound periderm. These accumulations suggest major roles for
Mg, P and K in the non-specific response of Sitka spruce both to wounding, possibly as co-factors to enzymes and energy utilisation.
The LA-ICP-MS method developed in this work proved useful to study spatial element distribution across bark samples and has
great potential for applications in other areas of plant pathology research. 相似文献
996.
997.
The ESR dose values of two human tooth enamel fragments were measured in 10° steps with an automated goniometer. ESR spectra were deconvoluted using four Gaussian peaks. The central region of the spectra is interfered with by at least one additional line which yields significantly lower dose values than the central, apparently axial region. There is a clear relationship between dose and width of the deconvoluted axial peaks which is attributable to incomplete separation between the axial and interfering peaks. A simple model is presented that coherently explains all observations. We conclude that deconvolution is necessary for the estimation of the most likely dose value of enamel pieces. 相似文献
998.
喷墨打印工艺是新兴的有机电子器件制造核心技术之一,而聚合有机半导体材料的选择从一定程度上决定了其可打印性和所制造器件的工作性能,因此变得极其重要。本文对PTAA(Polytriarylamine)这种聚合有机半导体材料进行了研究。用PTAA喷墨打印技术制备出了具有一定MOSFET器件特性的有机晶体管(OFET)并对其电学特性进行测试分析,利用红外光谱技术对PTAA材料在器件工作中所表现出的早期失效现象进行研究。 相似文献
999.
Paul Afolabi Mark Wright Steve A. Wootton Alan A. Jackson 《Isotopes in environmental and health studies》2013,49(3):346-356
This study determined the rates of 13C-aminopyrine metabolism in patients with varying degrees of liver cirrhosis as defined by clinical scores. Twenty-five cirrhotic patients and 18 healthy subjects underwent a 13C-aminopyrine breath test. The cumulative per cent dose recovery (cPDR) of 13C on breath expressed as a percentage of the administered dose at 2 h was significantly lower in cirrhotic patients than in healthy subjects (median: 1.7% versus 9.0%; p<.0001). Significant inverse associations between cPDR at 2 h and the model for end-stage liver disease score, Child–Pugh score, international normalised ratio and bilirubin (all p<.05), but not alanine aminotransferase or alkaline phosphatase were observed in the cirrhotic patients. Taking each biochemical marker independently, cirrhotic patients with normal biochemistry had a significantly lower cPDR at 2 h than healthy subjects (all p<.05). Differences in 13C-aminopyrine metabolism were evident in cirrhotic patients with less severe disease and may mark hepatic dysfunction when conventional biochemical markers appear unchanged. 相似文献
1000.
Xin Gai Yi Yu Bart Kuyken Pan Ma Steve J. Madden Joris Van Campenhout Peter Verheyen Gunther Roelkens Roel Baets Barry Luther‐Davies 《Laser \u0026amp; Photonics Reviews》2013,7(6):1054-1064
The wavelength dependence of the nonlinear absorption and the third order nonlinear refraction of crystalline silicon between m and m as well as at m have been measured. It was found that at all wavelengths multi‐photon and free carrier absorption can be significant. In particular nonlinear absorption can affect silicon devices designed for the mid‐infrared that require strong nonlinear response, such as for the generation of a supercontinuum. 相似文献