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排序方式: 共有266条查询结果,搜索用时 15 毫秒
21.
The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain. 相似文献
22.
Tommy Elfving 《BIT Numerical Mathematics》1998,38(2):275-282
Iterative methods applied to the normal equationsA
T
Ax=A
T
b are sometimes used for solving large sparse linear least squares problems. However, when the matrix is rank-deficient many
methods, although convergent, fail to produce the unique solution of minimal Euclidean norm. Examples of such methods are
the Jacobi and SOR methods as well as the preconditioned conjugate gradient algorithm. We analyze here an iterative scheme
that overcomes this difficulty for the case of stationary iterative methods. The scheme combines two stationary iterative
methods. The first method produces any least squares solution whereas the second produces the minimum norm solution to a consistent
system.
This work was supported by the Swedish Research Council for Engineering Sciences, TFR. 相似文献
23.
Dr. Walter T. Ralston Dr. Gérôme Melaet Tommy Saephan Prof. Gabor A. Somorjai 《Angewandte Chemie (International ed. in English)》2017,56(26):7415-7419
The Fischer–Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer–Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H2/CO=2. Large differences in carbon coverage (ΘC) were observed for the two catalysts: the 4.3 nm Co catalyst has a ΘC less than one while the 9.5 nm Co catalyst supports a ΘC greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B5-B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes. 相似文献
24.
Tommy Gustafsson 《Archive for Rational Mechanics and Analysis》1986,92(1):23-57
This paper studies Lp-estimates for solutions of the nonlinear, spatially homogeneous Boltzmann equation. The molecular forces considered include inverse kth-power forces with k > 5 and angular cut-off.The main conclusions are the following. Let f be the unique solution of the Boltzmann equation with f(v,t)(1 + ¦v2¦)(s
1
+ /p)/2 L1, when the initial value f
0 satisfies f
0(v) 0, f
0(v) (1 + ¦v¦2)(s
1
+ /p)/2 L1, for some s1 2 + /p, and f
0(v) (1 + ¦v¦2)s/2 Lp. If s 2/p and 1 < p < , then f(v, t)(1 + ¦v¦2)(s s
1)/2 Lp, t > 0. If s >2 and 3/(1+ ) < p < , thenf(v,t) (1 + ¦v¦2)(s(s
1
+ 3/p))/2 Lp, t > 0. If s >2 + 2C0/C1 and 3/(l + ) < p < , then f(v,t)(1 + ¦v¦2)s/2 Lp, t > 0. Here 1/p + 1/p = 1, x y = min (x, y), and C0, C1, 0 < 1, are positive constants related to the molecular forces under consideration; = (k – 5)/ (k – 1) for kth-power forces.Some weaker conclusions follow when 1 < p 3/ (1 + ).In the proofs some previously known L-estimates are extended. The results for Lp, 1 < p < , are based on these L-estimates coupled with nonlinear interpolation. 相似文献
25.
Smyth WF Morgan JL O'Kane E Millar TJ Ramachandran VN 《Rapid communications in mass spectrometry : RCM》2011,25(9):1308-1314
Electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) has been used for characterisation of a selection of naturally occurring and synthetic coumarins from different structural classes. The product ions, suggested in earlier studies by electrospray ionisation ion trap mass spectrometry (ESI-MS(n)), are unequivocally established for the representative coumarins by virtue of accurate mass measurement. Synthetic coumarins that are unsubstituted in the heterocyclic ring give rise to a major product ion by loss of CO(2), whereas those substituted in the heterocyclic ring generally undergo alternative fragmentation releasing neutral species such as ketene or methyl ketene. Naturally occurring coumarins, unsubstituted in the heterocyclic ring and substituted in the benzene ring with chains or rings of hydrocarbons and oxygen, principally fragment at the side chain releasing unsaturated hydrocarbons. The ESI-QTOF-MS/MS behaviour of some naturally occurring and synthetic quinolines which are structurally similar or fragment similarly are included where appropriate. 相似文献
26.
Tommy Sonne Alstrøm Mads Peter Sørensen Niels Falsig Pedersen Søren Madsen 《Acta Appl Math》2011,115(1):63-74
The time-dependent Ginzburg-Landau equation is solved numerically for type-II superconductors of complex geometry using the
finite element method. The geometry has a marked influence on the magnetic vortex distribution and the vortex dynamics. We
have observed generation of giant vortices at boundary defects, suppressing the superconducting state far into the superconductor. 相似文献
27.
28.
On Vervaat's sup vague topology 总被引:2,自引:0,他引:2
Tommy Norberg 《Arkiv f?r Matematik》1990,28(1):139-144
29.
Summary A series of apomorphine congeners has been studied with respect to their ability to mimic the structural requirements of the dopamine pharmacophore in the potent and stereoselective dopamine receptor agonist (R)-apomorphine. Conformational energies of the mimicking structures calculated by molecular mechanics (MMP2) correlate well with the observed biological activities. 相似文献
30.
This article builds on two previous ones in which we presented the processes of construction and consolidation of one student's knowledge structures about comparisons of infinite sets, according to a recently proposed theory of abstraction. In the present article, we show that under slight variations of context, knowledge structures that have apparently been well-consolidated may become inactive and subordinate to more primitive ones. 相似文献