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81.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
82.
J. Escudi C. Couret H. Ranaivonjatovo J. Satge 《Coordination chemistry reviews》1994,130(1-2):427-480
During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution. 相似文献
83.
A. Hagfeldt S. Lunell H. O. G. Sieghbahn 《International journal of quantum chemistry》1994,49(2):97-104
The energy levels of small titanium oxide clusters [(TiO2)2, and (TiO2H)3, and (TiO2H)2] have been calculated using ab initio SCF methods. Both crystal and relaxed geometries have been considered. Systematic changes in the valencelevel structure resulting from geometry relaxation are found, which may be related to band-gap changes experimentally observed for small titanium oxide particles. In addition, a Ti? OH local surface state is found to be well described within a limited cluster model. © 1994 John Wiley & Sons, Inc. 相似文献
84.
85.
A method using capillary gel electrophoresis with laser-induced fluorescence detection is described which permits complete sequence determination of antisense DNA analogues of unknown sequence. This method, originally created as a tool to confirm the sequence of antisense oligonucleotides being developed as therapeutic drugs, utilizes data collected under a range of experimental conditions described by the Ogston model as applied to gel electrophoresis. A linear relationship independent of experimental conditions between the relative electrophoretic migration time and the oligonucleotide base number was observed and is shown to be consistent with a simplified version of this model and can be used to facilitate the sequence determination. 相似文献
86.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
87.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. 总被引:12,自引:0,他引:12
L T Cohen F W Rickards G M Clark 《The Journal of the Acoustical Society of America》1991,90(5):2467-2479
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation. 相似文献
88.
Summary In the analysis of discretization methods for stiff intial value problems, stability questions have received most part of the attention in the past.B-stability and the equivalent criterion algebraic stability are well known concepts for Runge-Kutta methods applied to dissipative problems. However, for the derivation ofB-convergence results — error bounds which are not affected by stiffness — it is not sufficient in many cases to requireB-stability alone. In this paper, necessary and sufficient conditions forB-convergence are determined.This paper was written while J. Schneid was visiting the Centre for Mathematics and Computer Science with an Erwin-Schrödinger stipend from the Fonds zur Förderung der wissenschaftlichen Forschung 相似文献
89.
90.
Stability of a Model of Relativistic Quantum Electrodynamics 总被引:1,自引:0,他引:1
The relativistic “no pair” model of quantum electrodynamics uses the Dirac operator, D(A) for the electron dynamics together with the usual self-energy of the quantized ultraviolet cutoff electromagnetic field
A– in the Coulomb gauge. There are no positrons because the electron wave functions are constrained to lie in the positive
spectral subspace of some Dirac operator, D, but the model is defined for any number, N, of electrons, and hence describes a true many-body system. In addition to the electrons there are a number, K, of fixed nuclei with charges ≤Z. If the fields are not quantized but are classical, it was shown earlier that such a model is always unstable (the ground
state energy E=−∞) if one uses the customary D(0) to define the electron space, but is stable (E > − const.(N+K)) if one uses D(A) itself (provided the fine structure constant α and Z are not too large). This result is extended to quantized fields here, and stability is proved for α= 1/137 and Z≤ 42. This formulation of QED is somewhat unusual because it means that the electron Hilbert space is inextricably linked
to the photon Fock space. But such a linkage appears to better describe the real world of photons and electrons.
Received: 8 September 2001 / Accepted: 18 March 2002 相似文献