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91.
Functional magnetic resonance imaging with intermolecular multiple-quantum coherences 总被引:4,自引:0,他引:4
Richter W Richter M Warren WS Merkle H Andersen P Adriany G Ugurbil K 《Magnetic resonance imaging》2000,18(5):489-494
For the first time, we demonstrate here functional magnetic resonance imaging (fMRI) using intermolecular multiple-quantum coherences (iMQCs). iMQCs are normally not observed in liquid-state NMR because dipolar interactions between spins average to zero. If the magnetic isotropy of the sample is broken through the use of magnetic field gradients, dipolar couplings can reappear, and hence iMQCs can be observed. Conventional (BOLD) fMRI measures susceptibility variations averaged over each voxel. In the experiment performed here, the sensitivity of iMQCs to frequency variations over mesoscopic and well-defined distances is exploited. We show that iMQC contrast is qualitatively and quantitatively different from BOLD contrast in a visual stimulation task. While the number of activated pixels is smaller in iMQC contrast, the intensity change in some pixels exceeds that of BOLD contrast severalfold. 相似文献
92.
93.
We derive explicit, uniform, a priori interior Hessian and gradient estimates for special Lagrangian equations of all phases
in dimension two.
Y. Yuan is partially supported by an NSF grant. 相似文献
94.
Let K be a compact convex subset of a separated locally convex space (over R) and let Ap(K) denote the space of all continuous real-valued affine mappings defined on K, endowed with the topology of pointwise convergence on the extreme points of K. In this paper we shall examine some topological properties of Ap(K). For example, we shall consider when Ap(K) is monolithic and when separable compact subsets of Ap(K) are metrizable. 相似文献
95.
Warren Wm. McGovern 《Journal of Pure and Applied Algebra》2008,212(2):340-348
Elementary divisor domains were defined by Kaplansky [I. Kaplansky, Elementary divisors and modules, Trans. Amer. Math. Soc. 66 (1949) 464-491] and generalized to rings with zero-divisors by Gillman and Henriksen [L. Gillman, M. Henriksen, Some remarks about elementary divisor rings, Trans. Amer. Math. Soc. 82 (1956) 362-365]. In [M.D. Larsen, W.J. Lewis, T.S. Shores, Elementary divisor rings and finitely presented modules, Trans. Amer. Math. Soc. 187 (1) (1974) 231-248], it was also proved that if a Hermite ring satisfies (N), then it is an elementary divisor ring. The aim of this article is to generalize this result (as well as others) to a much wider class of rings. Our main result is that Bézout rings whose proper homomorphic images all have stable range 1 (in particular, neat rings) are elementary divisor rings. 相似文献
96.
97.
98.
The reactions of the hydroxyl radical (at low pH) and SO4−. have been employed to oxidize a number of phenyl-substituted alcohols in aqueous solution; ESR spectroscopy has been employed
to study directly the radicals formed by fragmentation of first-formed radical-cations. Examples of deprotonation (to give
benzyl radicals), Cα−Cβ bond scission (e.g. PhCH2CH2OH to PhCH2
.) and longer-range fragmentation (e.g. PhCH2CH2CMe2OH to PhCH2CH2
.) are described and discussed: evidence is obtained for intramolecular nucleophilic attack as a route for overall electron-transfer
from side-chain to aromatic ring. Solvation of the proton and of oxygen-conjugated carbonium ions is thought, at least in
part, to account for differences between fragmentations induced in the gaseous and aqueous phases. 相似文献
99.
Maroufi B. Laghmach R. EL Hadfi H. Daoud M. 《International Journal of Theoretical Physics》2021,60(8):3103-3114
The quantum Fisher information defined via the symmetric logarithmic derivative and the skew information are two different aspects describing the information contents of quantum mechanical density operators. They are considered as natural generalizations of the classical Fisher information and constitute key ingredients in the emerging field of quantum metrology. In this paper, we give the analytical expression of quantum Fisher information and skew information for two-qubit system prepared in a two-qubit state of X type.
相似文献100.
Amanda D. French Hannah M. Ashbaugh Gary Steinmetz Melanie Barnes Warren C. Conway David M. Klein 《International journal of environmental analytical chemistry》2017,97(6):499-507
The S.M.A.R.T. (small mass, affordable, rapid, transfer-less) digestion method was developed to determine heavy metal concentrations in small sample masses. The S.M.A.R.T. digestion method is a hot water bath digestion where sample digestion and dilution are performed in the original sample tube. This method is faster than the typical methods used and reduces potential sources of error. Masses as small as 0.01 g have been digested and analysed using this method. The preparation and digestion time is reduced from 10 h to less than 4 h. Acid volumes are reduced from millilitres to microlitres and the only disposable supplies needed are sample tubes and pipette tips. Method accuracy was determined by digesting seven replicates of two standard reference materials using the S.M.A.R.T. method and analysing samples by inductively coupled plasma mass spectrometry. The S.M.A.R.T. digestion method was found to provide excellent recoveries for Al (76 ± 2.7%), Mn (99 ± 11%), Co (92 ± 17%), Ni (93 ± 28%), Cu (109 ± 33%), Zn (97 ± 7.1%), As (108 ± 20%), Sr (90 ± 12%), Mo (84 ± 23%), Ag (91 ± 1.8%), Cd (95 ± 6.2%), Sn (139 ± 52%) and Pb (95 ± 22%). This study has successfully developed an efficient and reproducible digestion method for heavy metal determination in limited biomass samples. 相似文献