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Robert S. Van Dyck Jr. Steven L. Zafonte Paul B. Schwinberg 《Hyperfine Interactions》2001,132(1-4):163-175
Based on the use of a single ion, isolated at the center of a cryogenically cooled Penning trap, an environment is produced
which makes this mass spectrometer remarkably free of systematic errors. The most notable developments in our quest for an
ultra-high accuracy instrument were (a) the compensation of the trapping potential, (b) the discovery that motional sidebands
could manipulate radial energies, (c) the use of multiply-charged ions that could improve signal-to-noise, and (d) the use
of an ultra-stable superconducting magnet/cryostat system with drift <0.010 ppb/h. The dominant systematic errors are associated
with radial electric fields caused by image charges in the trap electrodes and with the rf-electrical drive field used to
determine the harmonic axial resonance. To illustrate the potential of this improved spectrometer, the four-fold improved
measurement of the proton's mass and the eight-fold improved measurement of oxygen's atomic mass will be described.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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SL Mironov E Skorova G Taschenberger N Hartelt VO Nikolaev MJ Lohse S Kügler 《BMC neuroscience》2009,10(1):29-11
Background
cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca2+ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before. 相似文献3.
The University of Washington Penning Trap Mass Spectrometer (UW-PTMS) is now producing measurements with uncertainties approaching
10 parts per trillion (ppt). We have recently published (Van Dyck, Jr. et al., Int J Mass Spectrom 251:231–242, 2006) detailed analysis of several systematic shifts which can be important at this level of accuracy. Experimental studies of
these effects in our older PTMS, combined with preliminary analysis of 2H data, and re-analysis of the previously reported 4He (Van Dyck, Jr. et al., Phys Rev Lett 92:220802/1, 2004) and 16O (Van Dyck, Jr. et al., Hyperfine Interact 132:163–175, 2001) data, gives more accurate atomic mass values for 16O, 4He, and 2H. Currently we are taking data for a new measurement of the 3He atomic mass, and working on some improvements to the PTMS, including a new amplifier system for phase-sensitive detection
of the ion’s axial motion, and a new computer-controlled ultra-stable voltage source for the Penning trap’s ring electrode,
used to adjust the ion’s axial frequency. These new systems will allow us to simultaneously manipulate individual ions in
two nearby Penning traps, and some sources of noise will be the same for both traps. We plan to investigate several techniques
which should reduce measurement time and improve accuracy by working with the two ions simultaneously.
This material is supported by the National Science Foundation under Grant No. 0353712. 相似文献
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Van Dyck RS Zafonte SL Van Liew S Pinegar DB Schwinberg PB 《Physical review letters》2004,92(22):220802
The atomic masses of the alpha particle and 4He have been measured by means of a Penning trap mass spectrometer which utilizes a frequency-shift detector to observe single-ion cyclotron resonances in an extremely stable 6.0 T magnetic field. The present resolution of this instrument approaches 0.01 ppb [10 ppt (parts per trillion)] and is limited primarily by the effective stability (<5 ppt/h) of the magnet over hundreds of hours of observation. The leading systematic shift [at -202(9) ppt] is due to the image charge located in the trap electrodes. The new value for the atomic mass of the alpha particle is 4 001 506 179.147(64) nu and the corresponding value for the mass of 4He is 4 002 603 254.153(64) nu (nu=10(-9) u). The 16 ppt uncertainty is at least 20 times smaller than any previous determination. 相似文献
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PF Hendrix SL Lachnicht MA Callaham X Zou 《Rapid communications in mass spectrometry : RCM》1999,13(13):1295-1299
Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used (13)C and (15)N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less (15)N enrichment ((15)N = 3-6 per thousand) than exotic Pontoscolex corethrurus ((15)N =7-9 per thousand) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in (15)N enrichment ((15)N = 6-9 per thousand), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in (15)N than those in the forest sites, but more highly enriched in (13)C suggesting assimilation of C from the predominant C(4) grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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