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排序方式: 共有146条查询结果,搜索用时 15 毫秒
41.
Eric B. Monroe Beth Anne Koszczuk Jenna L. Losh John C. Jurchen Jonathan V. Sweedler 《International journal of mass spectrometry》2007,260(2-3):237
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has been used for the discovery of hundreds of novel cell to cell signaling peptides. Beyond its advantages of sensitivity and minimal sample preparation requirements, MALDI MS is attractive for biological analyses as high quality mass spectra may be obtained directly from specific locations within prepared tissue sections. However, due to the large quantity of salts present in physiological tissues, these mass spectra often contain many adducts of cationic salts such as sodium and potassium, in addition to the molecular ion [M + H]+. To reduce the presence of cation adducts in MALDI mass spectra obtained directly from tissues, we present a methodology that uses a slow condensation procedure to enable the formation of distinct regions of matrix/analyte crystals and cation (salt) crystals. Secondary ion mass spectrometric imaging suggests that the salts and MALDI matrix undergo a mutually exclusive crystallization process that results in the separation of the salts and matrix in the sample. 相似文献
42.
Ron S. Dickson Jenna Bowen Eva M. Campi W. Roy Jackson Catrin A. M. Jonasson Felicity J. McGrath Daniel J. Paslow Anastasios Polas Paul Renton Serafino Gladiali 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):133-146
Four rhodium-based catalyst systems
1,
2,
3, and [Rh(OAc)2]2/PPh3 have been used in the hydroformylation of 1-hexene, styrene and some phosphino-, amino- and amido-alkenes. In general the catalysts showed very similar reactivity and selectivity. 相似文献
43.
From laser-induced line narrowing to electro- magnetically induced transparency: closed system analysis 总被引:1,自引:0,他引:1
The laser-induced line-narrowing effect, discovered more than thirty years ago, can also be applied to recent studies in high
resolution spectroscopy based on electromagnetically induced transparency. In this paper we first present a general form of
the transmission width of electromagnetically induced transparency in a homogeneously broadened medium. We then analyze a
Doppler broadened medium by using a lorentzian function as the atomic velocity distribution. The dependence of the transmission
linewidth on the driving field intensity is discussed and compared to the laser-induced line-narrowing effect. This dependence
can be characterized by a parameter which can be regarded as “the degree of optical pumping.”
Received: 17 December 2001 / Published online: 15 January 2003
RID="*"
ID="*"Corresponding author. E-mail: hwang.Lee@jpl.nasa.gov
RID="**"
ID="**"Present address: Jet Propulsion Laboratory, MS 126-347, California Institute of Technology, Pasadena, CA 91109, USA 相似文献
44.
R. Bednar U. Herzig I. Schuster P. Schuster P. Wolschann 《Magnetic resonance in chemistry : MRC》1976,8(6):301-307
The n.m.r. spectra of some 1,2,2-trisubstituted cyclopropanes are reported. Coupling constants and chemical shifts of the cyclopropane protons and their dependence on substituent effects are discussed. Conformations of benzylcyclopropane derivatives are investigated by long range magnetic shielding. The concentration dependence of the n.m.r. spectra of some 1,3-diols is explained by inter- and intramolecular hydrogen bonding. 相似文献
45.
Jozef Bednar 《Experimental Mechanics》1967,7(2):85-90
The method of model curing is applicable to the analysis of plates. When the polymerization process is complete and model is unloaded, the deflection and the birefringence remain permanent. The stereometric method is used for evaluation of bending and torsion moments, and photoelastic method is used as a control method. The example given of the method of curing is a square plate supported at three points and loaded by a concentrated load. 相似文献
46.
McAlexander Harley R. Giles Stephen A. Crouch Rebecca A. Peel Hannah R. Jones Stacy Bednar Anthony J. Shukla Manoj K. 《Structural chemistry》2020,31(3):975-982
Structural Chemistry - Alternatives to legacy munitions and explosives, materials that feature increased stability against external stimuli without compromising their energetic yields are currently... 相似文献
47.
Paul E. Smaldino Marco A. Janssen Vicken Hillis Jenna Bednar 《The Journal of mathematical sociology》2017,41(1):26-45
Social identities are among the key factors driving behavior in complex societies. Signals of social identity are known to influence individual behaviors in the adoption of innovations. Yet the population-level consequences of identity signaling on the diffusion of innovations are largely unknown. Here we use both analytical and agent-based modeling to consider the spread of a beneficial innovation in a structured population in which there exist two groups who are averse to being mistaken for each other. We investigate the dynamics of adoption and consider the role of structural factors such as demographic skew and communication scale on population-level outcomes. We find that outgroup aversion can lead to adoption being delayed or suppressed in one group, and that population-wide underadoption is common. Comparing the two models, we find that differential adoption can arise due to structural constraints on information flow even in the absence of intrinsic between-group differences in adoption rates. Further, we find that patterns of polarization in adoption at both local and global scales depend on the details of demographic organization and the scale of communication. This research has particular relevance to widely beneficial but identity-relevant products and behaviors, such as green technologies, where overall levels of adoption determine the positive benefits that accrue to society at large. 相似文献
48.
NMR Crystallography of an Oxovanadium(V) Complex by an Approach Combining Multinuclear Magic Angle Spinning NMR,DFT, and Spin Dynamics Simulations
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Dr. Frédérique Pourpoint Jenna Yehl Mingyue Li Dr. Rupal Gupta Dr. Julien Trébosc Prof. Olivier Lafon Prof. Jean‐Paul Amoureux Prof. Tatyana Polenova 《Chemphyschem》2015,16(8):1619-1626
Bioinorganic vanadium(V) solids are often challenging for structural analysis. Here, we explore an NMR crystallography approach involving multinuclear 13C/51V solid‐state NMR spectroscopy, density functional theory (DFT), and spin dynamics numerical simulations, for the spectral assignment and the 3D structural analysis of an isotopically unmodified oxovanadium(V) complex, containing 17 crystallographically inequivalent 13C sites. In particular, we report the first NMR determination of C–V distances. So far, the NMR observation of 13C–51V proximities has been precluded by the specification of commercial NMR probes, which cannot be tuned simultaneously to the close Larmor frequencies of these isotopes (100.6 and 105.2 MHz for 13C and 51V, respectively, at 9.4 T). By combining DFT calculations and 13C–51V NMR experiments, we propose a complete assignment of the 13C spectrum of this oxovanadium(V) complex. Furthermore, we show how 13C–51V distances can be quantitatively estimated. 相似文献
49.
Marlier EE Tereniak SJ Ding K Milliken JE Mulliken JE Lu CC 《Inorganic chemistry》2011,50(19):9290-9299
The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as (iPr)DPDBFphos) has been metalated with transition metal dichlorides of zinc, cobalt, and nickel to yield ((iPr)DPDBFphos)MCl(2) complexes. Within these compounds, the diphosphine (iPr)DPDBFphos adapts a wide range of bite angles (115 to 180°) as determined by X-ray crystallography. A three-coordinate planar Ni(I) species was isolated from the reduction of ((iPr)DPDBFphos)NiCl(2) with KC(8). Low-temperature electron paramagnetic resonance (EPR) measurements of ((iPr)DPDBFphos)NiCl allow the determination of g values (2.09, 2.14, 2.37) and hyperfine coupling constants to two (31)P nuclei, A(iso) = 46 × 10(-4) cm(-1), and one (37)Cl/(35)Cl nucleus, A = (12, 0.7, 35) × 10(-4) cm(-1). Density functional theory (DFT) studies reveal the nature of the magnetic orbital to be d(xy), which has σ-antibonding and π(∥)-antibonding interactions with the phosphorus and chloride atoms, respectively. The monovalent nickel complex reacts with substrates containing C-X bonds; and in the case of vinyl chloride, a Ni(II) vinyl species ((iPr)DPDBFphos)Ni(CH═CH(2))Cl is generated along with the Ni(II) dichloride complex. The monovalent Ni(I) chloride is an active catalyst in the Kumada cross-coupling reaction of vinyl chloride and phenyl Grignard reagent. 相似文献
50.
Wolstenholme DJ Sirsch P Onut L Flogeras J Decken A McGrady GS 《Dalton transactions (Cambridge, England : 2003)》2011,40(33):8301-8303
The extended structures of [K(1-aza-18-crown-6)]BH(4) and its 18-crown-6 analogue exhibits significantly different primary and secondary stabilizing interactions. However, their respective ion pairs display similar cation-to-anion interactions, in spite of the differences in the nature of the crown ether ligand. 相似文献