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排序方式: 共有888条查询结果,搜索用时 281 毫秒
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Brian C. Sales V. O. Garlea M.B. Stone M. D. Lumsden S. E. Nagler D. Mandrus 《哲学杂志》2020,100(10):1204-1210
ABSTRACTSingle crystals of the underscreened Kondo ferromagnet Yb14MnSb11 were investigated using polarised neutron diffraction and magnetisation measurements. The magnitude and direction of the magnetisation at each of the 9 distinct crystallographic sites was measured using polarised neutron diffraction. A large moment of close to 4.2?μB was found at the unique Mn site. A compensating antiferromagnetic moment of ≈?0.5?μB was found to be distributed uniformly among the remaining Yb and Sb sites, which was not expected from a previous theoretical calculation. The compensating magnetisation, however, is consistent both in size and magnitude with the expected Kondo screening cloud. 相似文献
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The Hydrazine–O2 Redox Couple as a Platform for Organocatalytic Oxidation: Benzo[c]cinnoline‐Catalyzed Oxidation of Alkyl Halides to Aldehydes 下载免费PDF全文
Ilana B. Stone Dr. Janis Jermaks Dr. Samantha N. MacMillan Prof. Tristan H. Lambert 《Angewandte Chemie (International ed. in English)》2018,57(38):12494-12498
An organocatalytic oxidation platform that capitalizes on the capacity of hydrazines to undergo rapid autoxidation to diazenes is described. Commercially available benzo[c]cinnoline is shown to catalyze the oxidation of alkyl halides to aldehydes in a novel mechanistic paradigm involving nucleophilic attack, prototropic shift, and hydrolysis. The hydrolysis and reoxidation events occur readily with only adventitious oxygen and water. A survey of the scope of viable substrates is shown along with mechanistic and computational studies that give insight into this mode of catalysis. 相似文献
5.
M. R. Menlyadiev J. A. Stone G. A. Eiceman 《International Journal for Ion Mobility Spectrometry》2012,15(3):123-130
A tandem ion mobility spectrometer with two sequential differential mobility spectrometry (DMS) drift tubes and with detectors at ambient pressure is described and modes of operation are demonstrated. Separate but coordinated electronic control for each drift tube allows several modes of operation including: all ions passing; compensation voltage (CV) scanning; and ion selection over a narrow CV range. Any of these modes can be applied to each drift tube allowing several combinations of analytical measurements, analogous to tandem mass spectrometry, with ions entered into a gas atmosphere containing reagents between the mobility regions. Ions may be changed by cluster or displacement reactions and characterized in the second DMS analyzer. Proton bound dimers of compounds appearing near 0?V CV in DMS1 were isolated in DMS1, introduced into 1?% isopropanol vapors, and resolved at characteristic CV values in the DMS2. This is achieved with analyzer dimensions little greater than a single DMS instrument. 相似文献
6.
Sean A.C. McDowell C. Ruth Le Sueur A. David Buckingham Anthony J. Stone 《Molecular physics》2013,111(5):823-835
The integrated intensities of vibrational transitions depend on the magnitude of the derivatives of the dipole with respect to nuclear motion. Normally, the only reliable way to compute such derivatives is by tedious and expensive ab initio calculations. In this paper, we present a simplification for weakly bound complexes based on distributed schemes for describing the charge densities and polarizabilities of the monomers. Formulations based on both Cartesian and spherical harmonics are presented. The results for both these schemes agree exactly with each other, and qualitatively with full ab initio calculations for the hydrogen fluoride dimer, (HF)2. 相似文献
7.
H. Sukumar J. A. Stone T. Nishiyama C. Yuan G. A. Eiceman 《International Journal for Ion Mobility Spectrometry》2011,14(2-3):51-59
A paper spray ion source was combined with a drift tube operating at ambient pressure for mobility measurements of ions derived from pharmaceutical solutions. Paper spray ionization with solvent alone resulted in a mixture of ions convolved to a single peak with a reduced mobility of 2.19 cm2/Vs in the mobility spectrum. These were mass-identified principally as m/z 157, (MeOH)2(HCOOH)2H+ and m/z 129, (MeOH)4(H2O)H+ while pharmaceuticals with nitrogen bases formed MH+ product ions. The duration of response was governed by the volume of liquid added to the paper source and was limited by evaporation of solvent in gas at 58 °C venting the drift tube. Quantitative variation was attributed in part to morphologic changes in the tip of the paper spray source. This was associated with mass flow in the electrical discharge and not due alone to cycles of wetting and drying of the paper. Mobility spectra of chlorpromazine in urine, exhibited a single product ion peak and linear response was 30 to 500 ng with an estimated limit of detection of 1.5 ng. Ion flux could be prolonged by continuous addition of liquid and findings portend a combination of paper spray ionization IMS with paper chromatography. 相似文献
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E. G. Nazarov R. A. Miller E. V. Krylov J. A. Stone G. A. Eiceman 《International Journal for Ion Mobility Spectrometry》2009,12(3):81-90
Mixtures of n-alkanethiols, in solution with equi-molar amounts from 0.5 to 360 ng per compound, were determined using gas
chromatography (GC) with a differential mobility spectrometer, operated with a flow of air at ambient pressure, as the GC
detector. A homologous series of n-alkanethiols with carbon number from two to six showed baseline resolution in the GC separation
and positive and negative ion chromatograms were produced simultaneously for the alkanethiols. Differential mobility spectra
showed compensation voltages characteristic of each alkanethiol and plots of ion intensity, retention time, and compensation
voltage yield contour plots illustrating the second dimension of analytical selectivity provided by the detector. Another
yet undeveloped dimension of analytical information was found in the dependence of mobility coefficients on electric field.
Mass-analysis of ions from thiols showed a hydrogen abstracted ion, protonated monomers, and proton bound dimers. Linear ranges
were narrow and the minimum detectable limits were ~1 ng. Response in positive polarity provided a ten-fold improvement in
detection limits though spectra were more complex than for negative ions. In a methane-rich air atmosphere, intended to simulate
ambient air or the detection of leaks from natural gas pipelines, the response to thiols with negative ions was not degraded
by the methane up to 50% v/v, the highest level tested. 相似文献
10.
Derek Booth Jack Burkart Xiaodong Cao Max Hallgren Zachary Munro Jason Snyder Tom Stone 《分析论及其应用》2019,35(2):192-204
This paper will develop a Li-Yau-Hamilton type differential Harnack estimate for positive solutions to the Newell-Whitehead-Segel equation on R^n.We then use our LYH-differential Harnack inequality to prove several properties about positive solutions to the equation,including deriving a classical Harnack inequality and characterizing standing solutions and traveling wave solutions. 相似文献