排序方式: 共有27条查询结果,搜索用时 265 毫秒
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Oz E Deng S Katsouleas T Muggli P Barnes CD Blumenfeld I Decker FJ Emma P Hogan MJ Ischebeck R Iverson RH Kirby N Krejcik P O'Connell C Siemann RH Walz D Auerbach D Clayton CE Huang C Johnson DK Joshi C Lu W Marsh KA Mori WB Zhou M 《Physical review letters》2007,98(8):084801
The onset of trapping of electrons born inside a highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions of a Li plasma confined by He gas. Li plasma electrons support the wake, and higher ionization potential He atoms are ionized as the beam is focused by Li ions and can be trapped. As the wake amplitude is increased, the onset of trapping is observed. Some electrons gain up to 7.6 GeV in a 30.5 cm plasma. The experimentally inferred trapping threshold is at a wake amplitude of 36 GV/m, in good agreement with an analytical model and PIC simulations. 相似文献
2.
We determine the set of equations which describe the dynamics of electrons in the presence of a wave propagating in an active medium. Simulation results indicate that, even when virtually all the energy is drained from the medium, electrons remain trapped by the accelerating wave. In spite of saturation, gradients of a few GV/m may become available. 相似文献
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Siemann S Badiei HR Karanassios V Viswanatha T Dmitrienko GI 《Chemical communications (Cambridge, England)》2006,(5):532-534
The apparently paradoxical behaviour of facile exchange (kinetic lability) of tightly bound (thermodynamic stability) zinc ions in the enzyme IMP-1 metallo-beta-lactamase with Zn-68 and cadmium ions, as indicated by in-torch vaporization inductively-coupled plasma mass spectrometry (ITV-ICP-MS) and electrospray-ionization mass spectrometry (ESI-MS), is consistent with the involvement of a third metal ion in promoting Lewis acid/base type exchange processes. 相似文献
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Fluorescence characterization of the natural organic matter in deep ground waters from the Canadian Shield,Ontario, Canada 总被引:1,自引:0,他引:1
François Caron Karen Sharp-King Stefan Siemann D. Scott Smith 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):699-705
Deep groundwater samples from a deep borehole in the Canadian Shield, Ontario, Canada, have been analyzed by fluorometry,
to determine the difference in character of the natural organic matter (NOM) with depth. This work was done to obtain a set
of geochemical characteristics of deep groundwaters at the site. The fluorescence signal is a complex signature of excitation
and emission of light from fluorescent molecules which are part of all natural waters. Fluorescent components have characteristic
excitation/emission components, defined as a humic-like (C1), fulvic-like (C2), and protein-like (C3); these are found in
various proportions in natural samples. Changes in relative fluorescence intensities of these components have been used in
the past to determine the origin and/or processes of the NOM between sampling locations. In this work, six samples were taken
at different depths, from ~108 to 650 m below the surface in the borehole. The fluorescence signals of the samples showed
three main patterns: (1) the shallower samples (~108, 139 and 285 m) had a pattern similar to that of surface groundwaters,
dominated by components C1 and C2; (2) the samples in deep groundwaters (~620 and 650 m) had a weak overall signal, dominated
by component C3; finally (3) the mid-depth sample (~503 m) had a component pattern intermediate between the shallower and
deeper zones. This set of data is consistent with other data for the groundwaters from this borehole, such as chlorinity,
suggesting that the three sampling intervals represent three different types of groundwaters. 相似文献
6.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
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Cell-free extracts (lysates) from Escherichia coli were used for protein synthesis in vitro. Essential steps of the lysate preparation were modified and analyzed with respect to their impact on in vitro protein synthesis capacity, using the green fluorescent protein (GFP) as a target protein. Variably manufactured lysates of low, medium and higher protein synthesis activity, were examined by high resolution two-dimensional gel electrophoresis to determine whether the modifications result in substantial alterations in protein composition of the final lysate. The total number of proteins calculated from the gel maps did not vary for lysates with different activity and thus cannot serve as an evaluation parameter. Ribosomal proteins RP-S1, RP-L9, and RP-L10 were found in stoichiometric amounts for each of these lysates and in equal concentrations in comparison among the different lysates. Conversely, depending on the activity profiles, up to 7 different isoforms of the elongation factor EF-Ts were detected in the gel maps. 相似文献
8.
A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10–6 to 8.0 × 10–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery. 相似文献
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The renormalization of the magnon energies in disordered, isotropic ferromagnets is investigated in the Hartree approximation. An expression equivalent to the Keffer-Loudon-Bloch renormalization factor is obtained by replacing products of normal mode expansion coefficients by their weighted sample averages. The results of self-consistent calculations of the renormalization factor and the magnetization are reported for dilute bond and amorphous ferromagnets. 相似文献
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A continuous-flow technique has been developed to analyse the deltaD and delta(13)C values for CH(4) from gas samples, in a single run. This is achieved by splitting the sample gas stream and directing the streams simultaneously through a CuNiPt combustion reactor and an alumina pyrolysis reactor. The CO(2) from CH(4) combustion is trapped in a liquid nitrogen trap while the H(2) exiting the pyrolysis reactor is directed to the mass spectrometer for deltaD(CH4) determination. The CO(2) is then sublimed and directed to the mass spectrometer for delta(13)C(CH4) determination. Sample runs take approximately 10 minutes. This technique gives accurate delta(13)C(CH4) results to within +/-0.3-0.5 per thousand and deltaD(CH4) results to within +/-2-5 per thousand. Injection volumes between 0.5 and 2.5 microL of CH(4), equivalent to between 20 and 100 nmol CH(4), are required for accurate delta(13)C and deltaD analyses, respectively, using sample injection into a split flow with a split ratio of 10. This method provides rapid, accurate and reproducible results on multiple sample runs and is, therefore, an ideal method for analysing natural gas samples from a variety of sources. 相似文献