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991.
Bartucci R Guzzi R Marsh D Sportelli L 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,162(2):1618-379
Spin-echo decays of spin-labelled phospholipids have been recorded to study the chain dynamics in the low-temperature phases of dipalmitoyl phosphatidylcholine membranes with and without 50 mol% cholesterol. The phase-memory relaxation time, T(2M), depends on the position of spin-labelling in the sn-2 chain, and on the presence of cholesterol. A biphasic temperature dependence of T(2M) is obtained over the range 150-270 K. Echo-detected field-swept absorption EPR spectra were recorded as a function of the echo delay time, tau. The echo-detected EPR lineshapes show a strong dependence on tau, revealing anisotropic phase relaxation arising from torsional chain motions. Cholesterol has a large effect on torsional oscillations about the chain long axis. Small-amplitude chain motions in the low-temperature phases may be important for cryopreservation of membranes. 相似文献
992.
Copper, zinc and iron concentrations were determined in “aguardiente de Cocuy de Penca” (Cocuy de Penca firewater), a spirituous beverage very popular in the North-Western region of Venezuela, by flame atomic absorption spectrometry (FAAS). These elements were selected for their presence can be traced to the (illegal) manufacturing process of the aforementioned beverages. Linear and quadratic discriminant analysis (QDA), and artificial neural networks (ANNs) trained with the backpropagation algorithm were employed for estimating if such beverages can be distinguished based on the concentrations of these elements in the final product, and whether it is possible to assess the geographic location of the manufacturers (Lara or Falcón states) and the presence or absence of sugar in the end product. A linear discriminant analysis (LDA) performed poorly, overall estimation and prediction rates being 51.7% and 50.0%, respectively. A QDA showed a slightly better overall performance, yet unsatisfactory (estimation: 79.2%, prediction: 72.5%). Various ANNs, comprising a linear function (L) in the input layer, a sigmoid function (S) in the hidden layer(s) and a hyperbolic tangent function (T) in the output layer, were evaluated. Of the networks studied, the (3L:5S:7S:4T) gave the highest estimation (overall: 96.5%) and prediction rates (overall: 97.0%), demonstrating the superb performance of ANNs for classification purposes. 相似文献
993.
Rita Khanna 《Pramana》1983,20(6):503-515
Diffusex-ray scattering in the region between the Bragg peaks has been calculated for self-interstitials in zinc. The required lattice distortions are calculated by the Kanzaki method and the scattering contributions from all equivalent orientations of a defect configuration are averaged. It is shown that a measurement in the (110) plane can clearly establish the stable interstitial configuration. 相似文献
994.
995.
MNDO method is used to study the interaction of nitrogen and carbon monoxide molecules with a proton, hydrogen atom, hydride ion, hydrogen molecule ion and hydrogen molecule. Predicted geometries and heats of reaction of different complexes are presented. The wave functions are analyzed in terms of ground state charge distributions and overlap populations. Electronic effects accompanying complexation are also discussed. 相似文献
996.
Rita Meyer-Spasche 《Numerische Mathematik》1972,19(5):433-438
Summary This paper describes a method of solving the Liapounov equation (1)HM+M
*
H=2D, M in upper Hessenberg form,D diagonal. Initialising the first row of the matrixA arbitrarily, one can find (by solving equations with one unknown) the unknown elements ofA such that (2)AM+M
*
A
*
=2F, whereA differs from a Hermitian matrix only in that its diagonal elements need not be real.F is a diagonal matrix which is uniquely determined by the first row ofA. By solving Eq. (2) for several initial values one may generate several matricesA andF (in the most unfavourable case 2n–1A's andF's are needed) and superpose them to getn linearly independent Hermitian matricesH
j
andD
j
respectively for whichH
j
M+M
*
H
j
=2D
j
is valid. Then one can solve the real system
to obtain the solution
of Eq. (1).This work was performed under the terms of the agreement on association between the Max-Planck-Institut für Plasmaphysik and Euratom. 相似文献
997.
998.
A transducer is proposed that measures both temperature and strain by using two different strain gages. The theoretical basis
for designing such a transducer is developed. Experimental results indicate that the temperature signal can be measured satisfactorily.
Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 10–13. 相似文献
999.
Rita Gitik Mahan Mitra Eliyahu Rips Michah Sageev 《Transactions of the American Mathematical Society》1998,350(1):321-329
We say that the width of an infinite subgroup in is if there exists a collection of essentially distinct conjugates of such that the intersection of any two elements of the collection is infinite and is maximal possible. We define the width of a finite subgroup to be . We prove that a quasiconvex subgroup of a negatively curved group has finite width. It follows that geometrically finite surfaces in closed hyperbolic -manifolds satisfy the -plane property for some .
1000.
We present an algorithmic and combinatorial proof of the following well-known theorem, originally proved by Rohlin: Every closed orientable 3-manifold M3 bounds a simply connected orientable 4-manifold M4. More precisely, an edge-coloured graph representing M4 is obtained as the final result of a finite and well-determined sequence of admissible moves, starting from any given edge-coloured graph representing M3. 相似文献