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131.
We add fermions to an Abelian-gauged hidden sector. We show that the lightest can be the dark matter with the right thermal relic abundance, and discovery is within reach of upcoming dark matter detectors. We also show that these fermions change Higgs boson phenomenology at the Large Hadron Collider (LHC), and in particular could induce a large invisible width to the lightest Higgs boson state. Such an invisibly decaying Higgs boson can be discovered with good significance in the vector boson fusion channel at the LHC. 相似文献
132.
Pellett J Lukulay P Mao Y Bowen W Reed R Ma M Munger RC Dolan JW Wrisley L Medwid K Toltl NP Chan CC Skibic M Biswas K Wells KA Snyder LR 《Journal of chromatography. A》2006,1101(1-2):122-135
A general procedure is proposed for the rapid development of a reversed-phase liquid chromatographic (RP-LC) separation that is "orthogonal" to a pre-existing ("primary") method for the RP-LC separation of a given sample. The procedure involves a change of the mobile-phase organic solvent (B-solvent), the replacement of the primary column by one of very different selectivity, and (only if necessary) a change in mobile phase pH or the use of a third column. Following the selection of the "orthogonal" B-solvent, column and mobile phase pH, further optimization of peak spacing and resolution can be achieved by varying separation temperature and either isocratic %B or gradient time. The relative "orthogonality" of the primary and "orthogonal" RP-LC methods is then evaluated from plots of retention for one method versus the other. The present procedure was used to develop "orthogonal" methods for nine routine RP-LC methods from six pharmaceutical analysis laboratories. The relative success of this approach can be judged from the results reported here. 相似文献
133.
A bimolecular rate constant, kOH + dihydromyrcenol, of (38 ± 9) × 10?12 cm3 molecule?1 s?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 2,6‐dimethyl‐7‐octen‐2‐ol (dihydromyrcenol,) at 297 ± 3 K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, k, of approximately 2 × 10?18 cm3 molecule?1 s?1 was determined by monitoring the decrease in ozone (O3) concentration in an excess of dihydromyrcenol. To more clearly define part of dihydromyrcenol's indoor environment degradation mechanism, the products of the dihydromyrcenol + OH and dihydromyrcenol + O3 reactions were also investigated. The positively identified dihydromyrcenol/OH and dihydromyrcenol/O3 reaction products were acetone, 2‐methylpropanal (O?CHCH(CH3)2), 2‐methylbutanal (O?CHCH(CH3)CH2CH3), ethanedial (glyoxal, HC(?O)C(?O)H), 2‐oxopropanal (methylglyoxal, CH3C(?O)C(?O)H). The use of derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible dihydromyrcenol/OH and dihydromyrcenol/O3 reaction mechanisms based on previously published volatile organic compound/OH and volatile organic compound/O3 gas‐phase reaction mechanisms. © 2006 Wiley Periodicals, Inc. * 1 This article is a US Government work and, as such, is in the public domain of the United States of America Int J Chem Kinet 38: 451–463, 2006 相似文献
134.
Bristow AD Kundys DO García-Déniz AZ Wells JP Fox AM Skolnick MS Whittaker DM Tahraoui A Krauss TF Roberts JS 《Optics letters》2006,31(15):2284-2286
We demonstrate all-optical switching in an active two-dimensional photonic crystal waveguide, observing as large as 16 nm blueshifts of a leaky eigenmode at 839 nm and switching ratios of almost 70%. These results are larger than those previously observed in similar experiments performed on passive photonic crystal waveguides; the enhancement is due to resonant photogeneration of carriers by In(0.12)Al(0.2)Ga(0.68)As quantum wells in the core of the waveguide. The effective change in the refractive index of the structure is approximately10(-2), with a rise time of approximately1 ps and a decay time of approximately10 ps, potentially allowing high-speed switching and fast modulation rates. 相似文献
135.
Wells WA 《Chemistry & biology》2000,7(11):R205-R206
136.
F. Song Å. Monsen Z.S. Li E.-M. Choi J.L. MacManus-Driscoll J. Xiong Q.X. Jia E. Wahlström J.W. Wells 《Surface science》2012,606(23-24):1771-1776
The surface and near-surface chemical composition of BiFe0.5Mn0.5O3 has been studied using a combination of low photon energy synchrotron photoemission spectroscopy, and a newly developed maximum entropy finite element model from which it is possible to extract the depth dependent chemical composition. In the uppermost few unit cells, an overabundance of Bi, and a deficiency of Fe and Mn are observed. In deeper layers, the measurements are consistent with bulk-like stoichiometry.Additionally, a definitive identification of all the observed species together with their abundance and depth dependence is given, and the mixed Fe and Mn valencies are estimated. In addition to the expected bulk valencies Mn3 + and Fe3 +, some Fe2 + and a small amount of Mn4 + are also observed. The maximum entropy finite element model demonstrated here is also discussed in more general terms and its potential application to the broader field of perovskite thin films is made apparent. 相似文献
137.
Frequency measurements are given for the 0001-0000 and 0111-0110 bands of N2O from 1257 to 1340 cm?1. The measurements utilize heterodyne techniques by measuring small frequency differences between a tunable diode laser locked to the center of an N2O absorption line and harmonic combinations of frequencies of radiation from two CO2 Lamb-dip-stabilized lasers. The measurements are facilitated by the use of the CO laser as a transfer laser whose frequency is also measured. These measurements have been combined with other data to provide new band constants and frequency calibration tables for several band systems of N2O in the following regions; 1215 to 1340, 1816 to 1930, and 2135 to 2268 cm?1. A correction factor is also provided for existing calibration tables near 590 cm?1. 相似文献
138.
The kinetics of the solvolysis of the ion trans-[Coen2N3Cl]+ have been investigated at several temperatures in mixtures of water with t-butyl alcohol with concentrations of the latter ranging up to 50 vol% or a mol fraction of 0.16. Values for the enthalpy and entropy of activation show sharp changes with changing solvent composition which can be correlated with extrema in the physical properties of the mixture concerned with sharp changes in solvent structure. Plots of log(rate constant) against the reciprocal of the dielectric constant and against the Grunwald-Winstein Y factor are both curved. The application of a free energy cycle shows that the effect of changes in solvent structure on the solvolysis dominates on the cobalt(III) cation in the transition state over that on the cation in the initial state. 相似文献
139.
D. E. Wells J. de Boer L. G. M. T. Tuinstra L. Reutergardh B. Griepink 《Fresenius' Journal of Analytical Chemistry》1988,332(6):591-597
Summary This paper gives an account of the systematic, collaborative learning programme undertaken by a group of experienced analytical laboratories within the European Economic Community (EEC) to improve the state-of-the art in the determination of individual chlorobiphenyl congeners in different matrices in preparation for the certification exercises to produce two fish oils as certified reference materials (CRMs). The choice of individual CB congeners, the critical GC parameters necessary to optimise the chromatographic separation and quantification of the congener is given. An assessment is made of the methods of extraction, separation and clean-up of samples prior to gas chromatographic analysis.
Verbesserung der Analyse von Chlorbiphenylen vor der Zertifizierung von sieben CBs in zwei Fischölen相似文献
140.
Summary The results of optimizing Soxhlet and Simultaneous Distillation-Extraction (SSDE) procedures for the isolation of natural insecticides fromTagetes erecta, Tagetes patula, andTagetes minuta, members of theCompositae family, are presented. Extraction procedures were developed and validated that produced the extract with the highest degree of biocidal activity. The highest activity was obtained with extracts isolated by SSDE using methylene chloride. Initial work was carried out on a micro-SSDE. Preparative SSDE was used to provide large quantities of extracts for bioassays. Bioassays were used to govern optimization procedures usingAedes aegypti andAnopheles stephensi adults and larvae as target organisms.Tagetes minuta was determined to be the most active of the three species studied. Evaluation of activity and recovery versus extraction time was investigated. It was determined that an extraction time of ten hours resulted in the highest activity and over 90% recovery of the oils. Finally, supercritical fluid extraction of the flowers with CO2 was compared to SSDE.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday. 相似文献