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

The uptake of spectral and temporal cues in vowel perception is rapidly influenced by context

Speech perception is dependent on auditory information within phonemes such as spectral or temporal cues. The perception of those cues, however, is affected by auditory information in surrounding context (e.g., a fast context sentence can make a target vowel sound subjectively longer). In a two-by-two design the current experiments investigated when these different factors influence vowel perception. Dutch listeners categorized minimal word pairs such as /tɑk/–/taːk/ (“branch”–“task”) embedded in a context sentence. Critically, the Dutch /ɑ/–/aː/ contrast is cued by spectral and temporal information. We varied the second formant (F2) frequencies and durations of the target vowels. Independently, we also varied the F2 and duration of all segments in the context sentence. The timecourse of cue uptake on the targets was measured in a printed-word eye-tracking paradigm. Results show that the uptake of spectral cues slightly precedes the uptake of temporal cues. Furthermore, acoustic manipulations of the context sentences influenced the uptake of cues in the target vowel immediately. That is, listeners did not need additional time to integrate spectral or temporal cues of a target sound with auditory information in the context. These findings argue for an early locus of contextual influences in speech perception

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

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

Speaking rate and spectral context affect the Dutch /a/ - /aa/ contrast

Dutch minimal word pairs such as 'gaas'-'gas' ("gauze"-"gas") differ in durational and spectral aspects of their vowels. These cues, however, are interpreted relative to the context in which they are heard. In a fast context, an "a" sounds relatively longer and is more likely to be interpreted as "aa". Similarly, when low frequencies in a context are perceived as dominant, high frequencies in the "a" become more salient, again more often leading to perception of "aa". A categorization experiment in which durational and spectral cues to the vowels were varied confirmed that Dutch listeners use both dimensions to distinguish between "a" and "aa". In Experiment 2, words were presented in rate- and spectrally manipulated sentences. Listeners, as predicted, interpreted the vowels relative to the context. An eye-tracking experiment will investigate the time course of these context effects and thus inform theories of the role of context in speech recognition

Allophones, not phonemes in spoken-word recognition

We thank Nadia Klijn for helping to prepare and test participants in Experiment 1 and Rosa Franzke for help with Experiments 2 and 3. The second author is funded by an Emmy-Noether grant (nr. RE 3047/1-1) from the German Research Council (DFG). This work was also supported by a University of Malta Research Grant to the first author.What are the phonological representations that listeners use to map information about the segmental content of speech onto the mental lexicon during spoken-word recognition? Recent evidence from perceptual-learning paradigms seems to support (context-dependent) allophones as the basic representational units in spoken-word recognition. But recent evidence from a selective-adaptation paradigm seems to suggest that context-independent phonemes also play a role. We present three experiments using selective adaptation that constitute strong tests of these representational hypotheses. In Experiment 1, we tested generalization of selective adaptation using different allophones of Dutch /r/ and /l/ – a case where generalization has not been found with perceptual learning. In Experiments 2 and 3, we tested generalization of selective adaptation using German back fricatives in which allophonic and phonemic identity were varied orthogonally. In all three experiments, selective adaptation was observed only if adaptors and test stimuli shared allophones. Phonemic identity, in contrast, was neither necessary nor sufficient for generalization of selective adaptation to occur. These findings and other recent data using the perceptual-learning paradigm suggest that pre-lexical processing during spoken-word recognition is based on allophones, and not on context-independent phonemes.peer-reviewe

Selective attention to a specific talker does not change the effect of surrounding acoustic context

Spoken sentences contain considerable prosodic variation, for instance in their speech rate [1]. One mechanism by which the listener can overcome such variation is by interpreting the durations of speech sounds relative to the surrounding speech rate. Indeed, in a fast context, a durationally ambiguous sound is perceived as longer than in a slow context [2]. In abstractionist models of spoken word comprehension, this process – known as rate normalization – affects pre-lexical representations before abstract phonological representations are accessed [3]. A recent study [4] provided support for such an early perceptual locus of rate normalization. In that study, participants performed a visual search task that induced high (large grid) vs. low (small grid) cognitive load, while listening to fast and slow context sentences. Context sentences were followed by durationally ambiguous targets. Fast sentences were shown to bias target perception towards more ‘long’ target segments than slow contexts. Critically, changes in cognitive load did not modulate this rate effect. These findings support a model in which normalization processes arise early during perceptual processing; too early to be affected by attentional modulation. The present study further evaluated the cognitive locus of normalization processes by testing the influence of another form of attention: auditory stream segregation. Specifically, if listeners are presented with a fast and a slow talker at the same time but in different ears, does explicitly attending to one or the other stream influence target perception? The aforementioned model [4] predicts that selective attention should not influence target perception, since normalization processes should be robust against changes in attention allocation. Alternatively, if attention does modulate normalization processes, two participants, one attending to fast, the other to slow speech, should show different perception. Dutch participants (Expt 1: N=32; Expt 2: N=16; Expt 3: N=16) were presented with 200 fast and slow context sentences of various lengths, followed by a target duration continuum ambiguous between, e.g., short target “geven” /ˈxevə/ give vs. long target “gegeven” /xəˈxevə/ given (i.e., 20 target pairs differing presence/absence of unstressed syllable /xə-/). Critically, in Experiment 1, participants heard two talkers simultaneously (talker and location counter-balanced across participants), one (relatively long) sentence at a fast rate, and one (half as long) sentence at a slow rate (rate varied within participants). Context sentences were followed by ambiguous targets from yet another talker (Fig. 1). Half of the participants was instructed to attend to talker A, while the other half attended to talker B. Thus, participants heard identical auditory stimuli, but varied in which talker they attended to. Debriefing questionnaires and transcriptions of attended talkers in filler trials confirmed that participants successfully attended to one talker, and ignored the other. Nevertheless, no effect of attended rate was found (Fig. 2; p>.9), indicating that modulation of attention did not influence participants’ rate normalization. Control experiments showed that it was possible to obtain rate effects with single talker contexts that were either talker-incongruent (Expt 2) or talker-congruent (Expt 3) with the following target (Fig. 1). In both of these experiments, there was a higher proportion of long target responses following a fast context (Fig. 2). This shows that contextual rate affected the perception of syllabic duration and that talker-congruency with the target did not change the effect. Therefore, in line with [4], the current experiments suggest that normalization processes arise early in perception, and are robust against changes in attention

Nonlinear interference in a mean-field quantum model

Using similar nonlinear stationary mean-field models for Bose-Einstein Condensation of cold atoms and interacting electrons in a Quantum Dot, we propose to describe the original many-particle ground state as a one-particle statistical mixed state of the nonlinear eigenstates whose weights are provided by the eigenstate non-orthogonality. We search for physical grounds in the interpretation of our two main results, namely, quantum-classical nonlinear transition and interference between nonlinear eigenstates.Comment: RevTeX (pdfLaTeX), 7 pages with 5 png-figures include

Critical currents in Josephson junctions with macroscopic defects

The critical currents in Josephson junctions of conventional superconductors with macroscopic defects are calculated for different defect critical current densities as a function of the magnetic field. We also study the evolution of the different modes with the defect position, at zero external field. We study the stability of the solutions and derive simple arguments, that could help the defect characterization. In most cases a reentrant behavior is seen, where both a maximum and a minimum current exist.Comment: 17 pages with 16 figures, submitted to Supercond. Sci. Techno