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1.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
2.
Matrix extensions and eigenvalue completions, the generic case 总被引:2,自引:0,他引:2
William Helton Joachim Rosenthal Xiaochang Wang 《Transactions of the American Mathematical Society》1997,349(8):3401-3408
In this paper we provide new necessary and sufficient conditions for the so-called eigenvalue completion problem.
3.
4.
For the first time a comparative study of holographic recording in planarly oriented films of nematic and cholesteric azobenzene-containing polymers was performed. The influence of temperature and light intensity on the values of diffraction efficiencies of holographic gratings was investigated. The kinetics of grating relaxation at different temperatures was studied. It was shown that the helical supramolecular structure of cholesteric copolymer causes a significant decrease of the diffraction efficiency in comparison with the one observed for the nematic state of the homopolymer. 相似文献
5.
6.
Klaus Anderle Richard Birenheide Martin J. A. Werner Joachim H. Wendorff 《Liquid crystals》1991,9(5):691-699
Polarized light leads to an effective reorientation of the optic axis in the glassy state of liquid-crystalline side chain polymers containing azobenzene mesogenic groups, via a trans-cis and cis-trans isomerization. Using a combination of U V and IR dichroitic studies it is shown for copolymers consisting of chromophores (azobenzene) and non-chromophores (phenylbenzoate) that only the chromophores are reoriented by light as far as the glassy state is concerned. Individual chromophores are thus addressed by photoselection. Photoselection in the fluid nematic state, on the other hand, leads also to a reorientation of the non-chromophores. 相似文献
7.
Gekelman W. Maggs J.E. Pfister H. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(6):614-621
A series of experiments on the dynamic interaction of two current channels has been performed in the large plasma device, a laboratory device at UCLA. The two current channels are formed by coating the cathode source nonuniformly and then biasing it with respect to an anode 10 m away. The experiment consists of two phases, one in which a net current is drawn through the plasma, and one in which the net current is zero. The current channels twist about each other, merge, and evolve toward a force-free state when a net current is drawn through the plasma. When the net current is zero the interaction between the channels is greatly reduced. The dynamics of the system are dominated by electron pressure and associated electrostatic fields. However, as the currents twist, a small amount of magnetic helicity is generated. The helicity and its temporal rate of change are computed and found to compare within experimental uncertainty to the predicted rate 相似文献
8.
Joachim Käschel 《Proceedings Mathematical Sciences》1992,102(2):155-158
In Venkaiah [1] an algorithm for solving linear optimization problems based on the idea of the projective algorithm of Karmarkar,
is proposed. The essential simplification in the new algorithm is the use of a fixed projection operator. In this way the
algorithm requires onlyO(n
2
) operations to obtain a sufficient exact solution. In this note it is shown that in some special cases the algorithm of Venkaiah
yields a feasible solution that is far from the optimal one. 相似文献
9.
Beate Bussemer Klaus-Peter Schrder Joachim Sauer 《Solid state nuclear magnetic resonance》1997,9(2-4)
A recent shell-model potential parameterized on ab initio data is used for predicting the all-silica structures of zeolites MFI, MEI, MTW, TON, FAU and of α-quartz. Cluster models are defined around each site and the 29Si NMR shielding constants are calculated by ab initio techniques (GIAO-HF). Good agreement with observed 29Si NMR chemical shifts is found. Comparison is made with shifts calculated for observed structures. The structures predicted by the ab initio shell-model potential prove as accurate as the observed ones when judged on the quality of the calculated 29Si NMR spectra. 相似文献
10.
M. Froese C. Champagne J. R. Crespo López-Urrutia S. Epp G. Gwinner A. Lapierre J. Pfister G. Sikler J. Ullrich J. Dilling 《Hyperfine Interactions》2006,173(1-3):85-92
The precision of atomic mass measurements in a Penning trap is directly proportional to the charge state q of the ion and,
hence, can be increased by using highly charged ions (HCI). For this reason, charge breeding with an electron beam ion trap
(EBIT) is employed at TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) on-line facility in Vancouver, Canada. By bombarding
the injected and trapped singly charged ions with an intense beam of electrons, the charge state of the ions is rapidly increased
inside the EBIT. To be compatible with the on-line requirements of short-lived isotopes, very high electron beam current densities
are needed. The TITAN EBIT includes a 6 Tesla superconducting magnet and is designed to have electron beam currents and energies
of up to 5 A and 60 keV, respectively. Once operational at full capacity, most species can be bred into a He-like configuration
within tens of ms. Subsequently, the HCI are extracted, pass a Wien filter to reduce isobaric contamination, are cooled, and
injected into a precision Penning trap for mass measurement. We will present the first results and current status of the TITAN
EBIT, which has recently been moved to TRIUMF after assembly and commissioning at the Max-Planck-Institute (MPI) for Nuclear
Physics in Heidelberg, Germany. 相似文献