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The Pistol star
(1998)
The effects of rotation and stellar magnetic fields on the nebular shapes : LBV nebulae and PNe
(1998)
The evolution of helium white dwarfs : I. the companion of the millisecond pular PSR J1012+5307
(1998)
Spectrum formation in clumped stellar winds : consequences for the analyses of Wolf-Rayet spectra
(1998)
On the validity of the core-mass luminosity relation for TP-AGB stars with efficient dredge-up
(1998)
On the basis of a stochastic model of hopping transport in disordered solids we present results of simulations of the dark discharge of surface charged thin films considering the energetic distribution of the localised states within the sheet. A non- linear differential equation with suitable boundary and initial conditions describes the time evolution of the space charge. We suppose a Gaussian distribution of energies for the carrier transporting states with a standard deviation s. The arrival time of carriers at the rear electrode of the sandwich sample is studied in dependence on film thickness, initial surface charge, and energetic disorder. Our calculations confirm that the transit time increases indirect proportional with initial surface charge and proportional with the square thickness. For standard deviations of energetic distribution of 0.05 eV up to 0.25 eV the normalised transit time grows as s1.44. We discuss this in terms of the stochastic transport model.
Langmuir floating layers of two phthalocyanine derivatives, ytterbium bisphthalocyanine and tetra-tert-butyl nickel phthalocyanine, were investigated by means of compression isotherms, surface potential kinetics and Brewster angle microscopy (BAM) in order to study the influence of peripheral substituents on the structure and stability of these films and on their suitability for a subsequent transfer onto solid substrates. Specific substitutions that may lead to amphiphilic molecular units seem to play a key role in the development of well organised thin films prepared with this technique.
We demonstrate the simultaneous quantum state reconstruction of the spectral modes of the light field emitted by a continuous wave degenerate optical parametric amplifier. The scheme is based on broadband measurement of the quantum fluctuations of the electric field quadratures and subsequent Fourier decomposition into spectral intervals. Applying the standard reconstruction algorithms to each bandwidth-limited quantum trajectory, a "spectrum" of density matrices and Wigner functions is obtained. The recorded states show a smooth transition from the squeezed vacuum to a vacuum state. In the time domain we evaluated the first order correlation function of the squeezed output field, showing good agreement with theory.
The complex behaviour of cardiorespiratory dynamics is shown to be related to the interaction between several physiological oscillators. This study is based on electrocardiogram and respiratory flow data obtained from 3 different subjects during paced breathing at 10 different pacing cycle lengths ranging from 5 s to 12 s. Two different methods ideally suited for the analysis of synchronization pattern of coupled oscillators are applied: 1. Symbolic dynamics based on symbol coding adapted for the detection of respiratory modulation of cardiac parasympathetic activity discloses two regimes of different synchronization behaviour within the frequency area corresponding to the Arnold tongue of 1:1 frequency-locking between respiratory flow and respiratory heartbeat variation (respiratory sinus arrhythmia). 2. The analysis of the phase shift between respiratory flow and respiratory sinus arrhythmia indicates that synchronization is not a static but a dynamic phenomenon. The observed dependence of the phase shift on respiratory cycle length shows large inter-individual variation. These findings turn out to be further hints for the existence of an additional central oscillator in the frequency range of respiration interacting with the central respiratory oscillator driving mechanical respiration.
We prove the existence of nonlinear localized time-periodic solutions in a chain of symplectic mappings with nearest neighbour coupling. This is a class of systems whose behaviour can be seen as representation of a lattice of pendula. The effect of discrete time changes the mathematical as well as the numerical procedures. Applying the discrete version of Floquet theory eases and clarifies the procedure of proving the existence of the localized time-periodic solutions. As an extension of the concept of rotobreathers one can produce solutions which rotate at every site of the lattice. To consider these we use a general definition of localization.
Dynamics and thermodynamics of spread and adsorbed food protein layers at the water/air interface
(1998)
Grazing incidence x-ray diffraction (GIXD) measurements of uranyl arachidate (UO2A2) LB films
(1998)
Phasenkonjugierende Spiegel auf Basis der stimulierten Brillouin-Streuung in optischen Wellenleitern
(1998)
Surface light emitting diodes (SLEDs) with a polymer-on-top geometry were used to study the sensitivity of light emission to oxygen. In these devices, pre-fabricated electrodes were coated with a conjugated polymer, which was thus directly exposed to the environment. Oxygen caused an immediate ten-to hundred fold decrease in electroluminescence efficiency relative to that in nitrogen or argon. Above the voltage for light emission, there was a sharp increase in current. Removing the oxygen led to recovery of the light intensity over a period of minutes, but the current returned immediately to its lower, original level. The electroluminescence and photoluminescence spectra were identical and were unaltered in shape by oxygen exposure (only decreasing in size). However, photoluminescence was unaffected by oxygen alone. This result indicates that oxygen does not affect excitons directly, but rather influences an intermediate species on the path to exciton formation, one that is significant only in electroluminescence and not in photoluminescence. Under simultaneous exposure to oxygen and UV light, the photoluminescence irreversibly decreased, presumably due to photo-oxidation
Conjugated polymers are organic semiconducting materials that can emit light. These polymers have the advantages of being light, cheap, and easy to process, and in addition the band gap can be tailored. We report the microfabrication of surface light emitting diodes (SLEDs) on silicon substrates in which the electrodes are underneath the organic electroluminescent layer. Patterned electrodes are separated by a 2500Å-thick insulating layer of silicon oxide or are interdigitated with a separation of 10 or 20 µm; the luminescent polymer is spin-coated or solvent cast on top of the electrodes. This fabrication method is completely compatible with conventional silicon processing because the polymer is deposited last and the light is emitted from the upper surface of the diodes. Despite the large spacing between electrodes, and despite the absence of an evaporated top contact, the voltages required for light emission were not much greater than those used in conventional sandwich-type structures