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排序方式: 共有101条查询结果,搜索用时 15 毫秒
21.
22.
An amplitude-only measurement setup can measure the axial ratio and tilt angle of an elliptically polarized wave. During design, both the amplitude and phase of the linear components are needed. The equipment measures the amplitudes directly. A nomograph, using the well-known relationships between polarization components determines the phase of the vertical component relative to the horizontal. The value of the nomograph goes beyond the stated objective, because it shows the relationships between the variables. The nomograph gives both the requirements for good circularity, and the sensitivity of the various parameters 相似文献
23.
A design method for improving the efficiency and reduction of sidelobes in displaced-axis two-reflector antennas is presented. The method is based on an analysis of the geometrical-optics field transformation in the displaced-axis two-reflector arrangement. The principal difference of the displaced-axis antenna from the Cassegrain/Gregory two-reflector antenna is pointed out. While decreasing the level of illumination of the subreflector edge in the Cassegrain/Gregory antenna leads to decreasing the sidelobe levels, and, respectively, the efficiency of the antenna system, in the displaced-axis antenna, decreasing the level of illumination of the subreflector leads to an increased level of sidelobes and an essentially nonuniform amplitude distribution in the aperture. The aperture-amplitude-distribution dependence of the illumination level of the subreflector edge in displaced-axis antennas is much stronger than in Cassegrain/Gregory antennas 相似文献
24.
The article looks at the practical aspect of tolerances on antenna design. We all know that our designs need to work after the variations caused by manufacturing. Tight tolerances are costly. The author takes us inside the feed network of an array, and shows the effects of errors, at different levels of the network, on the sidelobe performance. We can then specify the different parts properly, and produce antennas at the lowest cost 相似文献
25.
P A Milligan 《Journal of chromatography. A》1992,576(1):121-128
A simple and sensitive liquid chromatographic method with ultraviolet detection is described for the determination of the nonsteroidal anti-inflammatory drug piroxicam and its major metabolites in human plasma, urine and bile. Separation of these components occurs on a reversed phase C10CN column with a mobile phase consisting of acetonitrile-water-sodium dihydrogenphosphate solution. The detection limit of the assay was 50 ng/ml with intra- and inter-assay coefficients of variation for piroxicam of the order of 2 and 5%, respectively. The assay linearity was good (typically r = 0.9999). This method can be readily utilised for clinical pharmacokinetic and mass-balance studies. 相似文献
26.
Wilson PF Milligan DB Lam LW Freeman CG Meot-Ner M McEwan MJ 《Journal of the American Society for Mass Spectrometry》2002,13(9):1028-1033
We report the results of a flowing afterglow ion source-selected ion flow tube study (FA-SIFT) of the reactions of the methoxymethyl cation, CH3OCH2+. Rate coefficients and product branching ratios are reported for twenty nine reagent molecules including those that constitute the major ingredients of air, the hydrocarbons CH4, C2H6, C3H8, n-C4H10, C2H2, C2H4, C3H4 (allene and propyne), C6H6, and the S-containing molecules H2S, CH3SH, C2H5SH, (CH3)2SH, and (C2H5)2SH. In addition, we examined the reactions with the N-containing molecules NH3, CH3NH2, (CH3)2NH, (CH3)3N, pyrrole, pyridine as well as CH3COCH3. The results can be summarized under three general reaction types: Reaction at the CH3 carbon, reaction at the CH2 carbon, and association. The results also indicate that the methoxymethyl cation can be used as a chemical ionization source for the detection of trace levels of S-containing compounds in saturated hydrocarbons. 相似文献
27.
Hatcher LQ Lee DH Vance MA Milligan AE Sarangi R Hodgson KO Hedman B Solomon EI Karlin KD 《Inorganic chemistry》2006,45(25):10055-10057
Employing a tetradentate N3S(thioether) ligand, LN3S, dioxygen reactivity of a copper(I) complex, [(LN3S)CuI]+ (1) was examined. In CH2Cl2, acetone (at -80 degrees C), or 2-methyltetrahydrofuran (at -128 degrees C), 1 reacts with O2 producing the end-on bound peroxodicopper(II) complex [{(LN3S)CuII}2(mu-1,2-O2(2-))]2+ (2), the first reported copper-dioxygen adduct with sulfur (thioether) ligation. Its absorption spectrum contains an additional low-energy feature (but not a Cu-S CT band) compared to the previously well-characterized N4 ligand complex, [{(TMPA)CuII}2(mu-1,2-O2(2-))]2+ (3) (TMPA = tris(2-pyridylmethyl)amine). Resonance Raman spectroscopy confirms the peroxo formulation {nu(O-O) = 817 cm-1 (16-18O2 Delta = 46 cm-1) and nu(Cu-O) = 545 cm-1 (16-18O2 Delta = 26 cm-1), in close analogy to that known for 3 {nu(O-O) = 827 cm-1 and nu(Cu-O) = 561 cm-1}. Direct evidence for thioether ligation comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 A}. 相似文献
28.
Milligan JR Aguilera JA Hoang O Ly A Tran NQ Ward JF 《Journal of the American Chemical Society》2004,126(6):1682-1687
By using gamma-irradiation in the presence of thiocyanate ions, we have generated guanyl radicals in plasmid DNA. These can be detected by using an Escherichia coli base excision repair endonuclease to convert their stable end products to strand breaks. The yield of enzyme-sensitive sites is strongly attenuated by the presence of micromolar concentrations of one of a series of singly substituted phenols, and it is possible to derive bimolecular rate constants for the reduction of DNA guanyl radicals by these phenols. More strongly reducing phenols were found to react more rapidly. This electron-transfer reaction also involves a proton transfer. By comparing the expected energetics of the reaction with the observed rate constants, the electron transfer is found to be mechanistically coupled with the proton transfer. 相似文献
29.
Wan‐Ping Hu Vaughan S. Langford Murray J. McEwan Daniel B. Milligan Malina K. Storer Jack Dummer Michael J. Epton 《Rapid communications in mass spectrometry : RCM》2010,24(12):1744-1748
The selectivity and sensitivity of selected ion flow tube mass spectrometry (SIFT‐MS) for individual breath analysis of haloamines has been improved by heating the flow tube in a commercial instrument to around 106°C. Data is presented showing the marked reduction in the number density of water clusters of product ions of common breath metabolites that are isobaric with the product ions from monochloramine and monobromamine that are used to monitor the haloamine concentrations. These results have direct relevance to the real‐time monitoring of chloramines in drinking water, swimming pools and food processing plants. However, once the isobaric overlaps from water cluster ions are reduced at the higher temperatures, there is no conclusive evidence showing the presence of haloamines on single breath exhalations in the mid parts per trillion range from examination of the breaths of volunteers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
30.
Xiaoyan Xia Bernard S. Crimmins Philip K. Hopke James J. Pagano Michael S. Milligan Thomas M. Holsen 《Analytical and bioanalytical chemistry》2009,395(2):457-463
Toxaphene is considered to be a problematic organochlorine pollutant because of its bioaccumulation potential and persistence
in aquatic environments. In this study, whole lake trout and walleye composites were used to evaluate two analytical techniques
for total toxaphene and selected congener analysis. The efficacy of using gas chromatography electron ionization tandem mass
spectrometry (GC-EI/MS/MS) and electron capture negative ionization mass spectrometry (GC-ECNI-MS) were compared. Although
the sensitivity using GC-ECNI-MS was approximately five times greater than GC-EI/MS/MS, the latter provided more consistent
inter-Parlar relative response factors (RRF). When using technical calibration mixtures, these results suggest a more accurate
total toxaphene measurement was obtained using the GC-EI/MS/MS method. Total toxaphene concentrations in lake trout composites
from both methods were highly correlated (R
2 = 0.985) with the MS/MS concentrations approximately half of those determined by ECNI, suggesting systematic high bias in
toxaphene concentrations when measured using GC-ECNI. 相似文献