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11.
Wang K Zhu Z Yang L Gao Y Liu W Zhang H Chai Y 《Rapid communications in mass spectrometry : RCM》2011,25(1):9-19
This work describes a novel methodology for unequivocal identification of chemical constituents in Zhimu‐Baihe herb‐pair (ZMBHHP). Compounds were removed from ZMBHHP by ultrasonic extraction with 70% ethanol, and then analyzed by fast high‐performance liquid chromatography (HPLC) coupled with time‐of‐flight mass spectrometry (TOFMS). The accurate‐mass capability of the TOF analyzer allowed reliable confirmation of the identity of the detected compounds, normally with mass errors below 3 ppm in routine analysis. This mass accuracy was sufficient to verify the elemental compositions of the chemical constituents in ZMBHHP. With dynamic adjustment of fragmentor voltage in TOFMS, an efficient ion transmission was achieved to obtain the best sensitivity and abundant fragmentation. By accurate mass measurements for each molecular ion and subsequent fragment ions, a reliable identification and differentiation of 24 saponins, 3 xanthones, 1 anthraquinone and 2 alkaloids was described here, including four groups of isomers. It is concluded that this fast and sensitive HPLC/ESI‐TOFMS technique is powerful in qualitative analysis of complex herbal medicines in terms of sensitivity, selectivity, resolving power, time savings and lower solvent consumption. Furthermore, the data gathered in this study may be helpful for understanding the synergistic nature of this herb pair in traditional Chinese medicine (TCM) and further pharmacokinetic studies of ZMBHHP. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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While aggregate reasoning is a core aspect of statistical reasoning, its development is a key challenge in statistics education. In this study we examine how students’ aggregate reasoning with samples and sampling (ARWSS) can emerge in the context of statistical modeling activities of real phenomena. We present a case study on the emergent ARWSS of two pairs of sixth graders (age 11–12) involved in statistical data analysis and informal inference utilizing TinkerPlots. The students’ growing understandings of various statistical concepts is described and five perceptions the students expressed are identified. We discuss the contribution of modeling to these progressions followed by conclusions and limitations of these results. While idiosyncratic, the insights contribute to the understanding of students’ aggregate reasoning with data and models, with regards to samples and sampling. 相似文献
14.
The rapid advance in molecular biology and nanotechnology opens up the possibility to explore the interface between biology and electronics at the single-molecule level. We focus on the organization of molecular electronic circuits. Interconnecting an immense number of molecular devices into a functional circuit and constructing a framework for integrated molecular electronics requires new concepts. A promising avenue relies on bottom-up assembly where the information for the circuit connectivity and functionality is embedded in the molecular building blocks. Biology can provide concepts and mechanisms for advancing this approach, but there is no straightforward way to apply them to electronics since biological molecules are essentially electrically insulating. Bridging the chasm between biology and electronics therefore presents great challenges. Circuit organization on the molecular scale is considered and contrasted with the levels of organization presented by the living world. The discussion then focuses on our proposal to harness DNA and molecular biology to construct the scaffold for integrated molecular electronics. DNA metallization is used to convert the DNA scaffold into a conductive one. We present the framework of sequence-specific molecular lithography based on the biological mechanism of homologous genetic recombination and carried out by the bacterial protein RecA. Molecular lithography enables us to use the information encoded in the scaffold DNA molecules for directing the construction of an electronic circuit. We show that it can lead all the way from DNA molecules to working transistors in a test-tube. Carbon nanotubes are incorporated as the active electronic components in the DNA-templated transistors. Our approach can, in principle, be applied to the fabrication of larger-scale electronic circuits. The realization of complex DNA-based circuits will, however, require new concepts and additional biological machinery allowing, for example, feedback from the electronic functionality to direct the assembly process and adaptation mechanisms. 相似文献
15.
The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement
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Dr. Sivil Kopilevich Dr. Hugo Gottlieb Dr. Keren Keinan‐Adamsky Prof. Dr. Achim Müller Prof. Ira A. Weinstock 《Angewandte Chemie (International ed. in English)》2016,55(14):4476-4481
In Nature, enzymes provide hydrophobic cavities and channels for sequestering small alkanes or long‐chain alkyl groups from water. Similarly, the porous metal oxide capsule [{MoVI6O21(H2O)6}12{(MoV2O4)30(L)29(H2O)2}]41? (L=propionate ligand) features distinct domains for sequestering differently sized alkanes (as in Nature) as well as internal dimensions suitable for multi‐alkane clustering. The ethyl tails of the 29 endohedrally coordinated ligands, L, form a spherical, hydrophobic “shell”, while their methyl end groups generate a hydrophobic cavity with a diameter of 11 Å at the center of the capsule. As such, C7 to C3 straight‐chain alkanes are tightly intercalated between the ethyl tails, giving assemblies containing 90 to 110 methyl and methylene units, whereas two or three ethane molecules reside in the central cavity of the capsule, where they are free to rotate rapidly, a phenomenon never before observed for the uptake of alkanes from water by molecular cages or containers. 相似文献
16.
Michael Grouchko Alexander Kamyshny Keren Ben-Ami Shlomo Magdassi 《Journal of nanoparticle research》2009,11(3):713-716
Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine
monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition
of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also
results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum
of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size
in the range of 5–50 nm. 相似文献
17.
We have constructed a compact room-temperature mid-infrared spectrometer and gas sensor, based on quasi-phase matched difference-frequency generation in periodically poled ferroelectric crystals of the KTiOPO4 family, namely: KTiOPO4, KTiOAsO4 and RbTiOAsO4. The wide tunabilty of the spectrometer (3.1–3.75 μm) enables us to cover an entire vibrational band of gases such as methane and nitrous oxide. The high spectral resolution (1 MHz) is used to investigate the spectral profile of the hyperfine components of a single rotational transition. The sensitivity of the described spectrometer is 75 parts per million. Applications of this technology include the detection of polluting or toxic gases, biomedical sensing, atmospheric research, volcanic monitoring and industrial process control. 相似文献
18.
S. F. J. Cox J. S. Lord S. P. Cottrell H. V. Alberto J. M. Gil J. Piroto Duarte R. C. Vilão A. Keren D. Prabhakaran 《Hyperfine Interactions》2004,158(1-4):313-316
Muonium centres in Cu2O, Ag2O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen
defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely
quasi-atomic (possibly deep acceptor), deep donor and shallow donor. 相似文献
20.
B. Nachumi A. Keren K. Kojima M. Larkin G.M. Luke J. Merrin O. Tchernyshöv W.D. Wu Y.J. Uemura Y. Fukuzumi K. Mizuhashi K. Takenaka S. Uchida 《Hyperfine Interactions》1997,105(1-4):125-130
We report the muon spin rotation experiments on Zn substituted La1-x Srx CuO4, for four zinc concentrations y=0.0,0.0025,0.005,0.01, at strontium concentrations x=0.15,0.20. We find that T_ c in the
optimally doped (x=0.15) and overdoped (x=0.20) 2:1:4 decreases linearly with increasing zinc concentration. Plotted against
the planar zinc concentration, the Tc’s of both series seem to fall on the same line. The superconducting carrier density/effective mass ratio, n_ s/m*, at first decreases linearly, rising above this line for higher zinc concentrations. This behavior may result from the localization
of carriers in an area \xiab around each zinc atom.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献