1,297 research outputs found
How Cooperative are the Dynamics in Tunneling Systems? A Computer Study for an Atomic Model Glass
Via computer simulations of the standard binary Lennard-Jones glass former we
have obtained in a systematic way a large set of close-by pairs of minima on
the potential energy landscape, i.e. double-well potentials (DWP). We analyze
this set of DWP in two directions. At low temperatures the symmetric DWP give
rise to tunneling systems. We compare the resulting low-temperature anomalies
with those, predicted by the standard tunneling model. Deviations can be traced
back to the energy dependence of the relevant quantities like the number of
tunneling systems. Furthermore we analyze the local structure around a DWP as
well as the translational pattern during the transition between both minima.
Local density anomalies are crucial for the formation of a tunneling system.
Two very different kinds of tunneling systems are observed, depending on the
type of atom (small or large) which forms the center of the tunneling system.
In the first case the tunneling system can be interpreted as a single-particle
motion, in the second case it is more collective
Lexical stress information modulates the time-course of spoken-word recognition
Segmental as well as suprasegmental information is used by Dutch listeners to recognize words. The time-course of the effect of suprasegmental stress information on spoken-word recognition was investigated in a previous study, in which we tracked Dutch listeners' looks to arrays of four printed words as they listened to spoken sentences. Each target was displayed along with a competitor that did not differ segmentally in its first two syllables but differed in stress placement (e.g., 'CENtimeter' and 'sentiMENT'). The listeners' eye-movements showed that stress information is used to recognize the target before distinct segmental information is available. Here, we examine the role of durational information in this effect. Two experiments showed that initial-syllable duration, as a cue to lexical stress, is not interpreted dependent on the speaking rate of the preceding carrier sentence. This still held when other stress cues like pitch and amplitude were removed. Rather, the speaking rate of the preceding carrier affected the speed of word recognition globally, even though the rate of the target itself was not altered. Stress information modulated lexical competition, but did so independently of the rate of the preceding carrier, even if duration was the only stress cue present
What is moving in silica at 1 K? A computer study of the low-temperature anomalies
Though the existence of two-level systems (TLS) is widely accepted to explain
low temperature anomalies in many physical observables, knowledge about their
properties is very rare. For silica which is one of the prototype glass-forming
systems we elucidate the properties of the TLS via computer simulations by
applying a systematic search algorithm. We get specific information in the
configuration space, i.e. about relevant energy scales, the absolute number of
TLS and electric dipole moments. Furthermore important insight about the
real-space realization of the TLS can be obtained. Comparison with experimental
observations is included
Ultraviolet and thermally stable polymer compositions
A class of polymers is provided, namely, poly(diarylsiloxy) arylazines. These polymers have a basic chemical composition which has the property of stabilizing the optical and physical properties of the polymer against the degradative effect of ultraviolet light and high temperatures. This stabilization occurs at wavelengths including those shorter than found on the surface of the earth and in the absence or presence of oxygen, making the polymers of the present invention useful for high performance coating applications in extraterrestrial space as well as similar applications in terrestrial service. The invention also provides aromatic azines which are useful in the preparation of polymers such as those of the present invention
Ultraviolet and thermally stable polymer compositions
A new class of polymers is provided, namely, poly (diarylsiloxy) arylazines. These novel polymers have a basic chemical composition which has the property of stabilizing the optical and physical properties of the polymer against the degradative effect of ultraviolet light and high temperatures. This stabilization occurs at wavelengths including those shorter than found on the surface of the earth and in the absence or presence of oxygen, making the polymers useful for high performance coating applications in extraterrestrial space as well as similar applications in terrestrial service. The invention also provides novel aromatic azines which are useful in the preparation of polymers such as those described
Metastability of persistent currents in trapped gases of atoms
We examine the conditions that give rise to metastable, persistent currents
in a trapped Bose-Einstein condensate. A necessary condition for the stability
of persistent currents is that the trapping potential is not a monotonically
increasing function of the distance from the trap center. Persistent currents
also require that the interatomic interactions are sufficiently strong and
repulsive. Finally, any off-center vortex state is shown to be unstable, while
a driven gas shows hysteresis.Comment: 7 pages, RevTex, 5 figure
Ultraviolet and thermally stable polymer compositions
Copolymers, produced from aromatic substituted aromatic azine-siloxane compositions, are thermally stable, solar ultraviolet light non-degradable by wavelengths shorter than those reaching earth surface
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