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排序方式: 共有80条查询结果,搜索用时 187 毫秒
1.
Ionization of aliphatic and aromatic aldehydes is improved by performing simultaneous chemical derivatization using 4-aminophenol to produce charged iminium ions during paper spray ionization. Accelerated reactions occur in the microdroplets generated during the paper spray ionization event for the tested aldehydes (formaldehyde, n-pentanaldehyde, n-nonanaldehyde, n-decanaldehyde, n-dodecanaldehyde, benzaldehyde, m-anisaldehyde, and p-hydroxybenzaldehyde). Tandem mass spectrometric analysis of the iminium ions using collision-induced dissociation demonstrated that straight chain aldehydes give a characteristic fragment at m/z 122 (shown to correspond to protonated 4-(methyleneamino)phenol), while the aromatic aldehyde iminium ions fragment to give a characteristic product ion at m/z 120. These features allow straightforward identification of linear and aromatic aldehydes. Quantitative analysis of n-nonaldehyde using a benchtop mass spectrometer demonstrated a linear response over 3 orders of magnitude from 2.5 ng to 5 μg of aldehyde loaded on the filter paper emitter. The limit of detection was determined to be 2.2 ng for this aldehyde. The method had a precision of 22%, relative standard deviation. The experiment was also implemented using a portable ion trap mass spectrometer. 相似文献
2.
Alula Melisew Tadele Krishnan Sriram Hendricks Nicolette R. Karamchand Leshern Blackburn Jonathan M 《Mikrochimica acta》2017,184(1):219-227
Microchimica Acta - The authors present a fast and sensitive surface-enhanced Raman spectroscopy (SERS) method for the determination of Mycobacterium smegmatis. It is based on the formation of... 相似文献
3.
Equivalent drag-reducing performance is observed with 3 M riblets in fully developed internal (pipe) and developing external (flat plate) flows. Drag reduction begins around h
+ = 3, peaks between 6 and 9% at about h
+ = 12, and becomes zero for a value of h
+ between 20 and 30. In laminar pipe flow no significant change in drag is observed with the 3 M riblets present. At high Reynolds numbers, after exhibiting fully rough behaviour, friction factors for the 3 M riblets are observed to monotonically decrease with increasing Reynolds number. 相似文献
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Hendricks K.J. Haworth M.D. Englert T. Shiffler D. Baca G. Coleman P.D. Bowers L. Lemke R.W. Spencer T.A. Arman M.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(3):320-325
The Air Force Research Laboratory RKO source has recently demonstrated the ability to convert electron beam power to RF power until the termination of the electron beam pulse, achieving a power of 1.5 GW at an energy of 170 J. These results represent an increase in power of 25-30% in power and energy extracted from this source. This paper discusses the principal research areas encountered in lengthening the RF pulse (FWHM) from 50 ns to the present 120 ns and the associated increase in the RF energy 相似文献
8.
Moreland L.D. Schamiloglu E. Lemke W. Korovin S.D. Rostov V.V. Roitman A.M. Hendricks K.J. Spencer T.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(5):554-565
The Sinus-6, a high-power relativistic repetitively-pulsed electron beam accelerator, is used to drive various slow wave structures in a BWO configuration in vacuum. Peak output power of about 550 MW at 9.45 GHz was radiated in an 8-ns pulse. We describe experiments which study the relative efficiencies of microwave generation from a two-stage nonuniform amplitude slow wave structure and its variations without an initial stage. Experimental results are compared with 2.5 D particle-in-cell computer simulations. Our results suggest that prebunching the electron beam in the initial section of the nonuniform BWO results in increased microwave generation efficiency, Furthermore, simulations reveal that, in addition to the backward propagating surface harmonic of the TM01 mode, backward and forward propagating volume harmonics with phase velocity twice that of the surface harmonic play an important role in high-power microwave generation and radiation 相似文献
9.
P. A. Westbrook J. F. Fellers M. Cakmak J. S. Lin R. W. Hendricks 《Journal of Polymer Science.Polymer Physics》1983,21(10):1913-1926
An investigation of the reflective component of small-angle x-ray scattering patterns of polystyrene crazes is performed. It is shown that the strong streak parallel to the tensile axis consists predominantly of reflected radiation, while the remaining pattern is composed entirely of diffracted radiation. X-ray reflection off unparallel regions of crazes is discussed and the nature of the reflection is also considered in terms of collimation quality. An analysis methodology based on craze tip angular distribution is proposed. 相似文献
10.
K. Petersen N. Thrane G. Trumpy R. W. Hendricks 《Applied physics. B, Lasers and optics》1976,10(1):85-90
We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of
1.5·1021 n/cm2 (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·1014 voids/cm3 with a mean diameter of 330 ?, as determined by both small-angle x-ray scattering and transmission electron microscopy. The
positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component
is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the
voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the
model of a positron state at the void surface. The positron diffusion coefficient appears to have aT
1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating
sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described
by a single component of 170 ps, the observed lifetime in unirradiated aluminum.
Research sponsored in part by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation. 相似文献