Showing papers by "Hermann Wagner published in 1999"
TL;DR: In this article, the β-relaxation intensity of o-terphenyl is shown to decay gradually upon annealing and disappears altogether in the equilibrium liquid state at T > Tg.
Abstract: A previous observation, which indicated that the β-relaxation intensity of o-terphenyl is sensitive to the thermal history, is substantiated by dielectric relaxation experiments. Unlike the β-processes of other materials, only the quenched glassy state of o-terphenyl displays this secondary relaxation feature. The β-intensity is observed to decay gradually upon annealing and disappears altogether in the equilibrium liquid state at T > Tg. We compare the case of o-terphenyl with the concomitant signatures of d-sorbitol, which represents the more typical case of a glass-former which exhibits the slow β-process also in the liquid state including the α−β-merging scenario. We also present data of this α−β-merging for d-sorbitol confined to pores of 5 nm diameter, indicating that no longer-ranged correlations are involved in the secondary process.
180 citations
TL;DR: It is shown that barn owls perceive subjective contours defined by grating gaps and phase-shifted abutting gratings, which suggest that the visual Wulst is important in contour-based form perception and exhibits a functional complexity analogous to mammalian extrastriate cortex.
Abstract: Robust form perception and underlying neuronal mechanisms require generalized representation of object boundaries, independent of how they are defined. One visual ability essential for form perception is reconstruction of contours absent from the retinal image. Here we show that barn owls perceive subjective contours defined by grating gaps and phase-shifted abutting gratings. Moreover, single-neuron recordings from visual forebrain (visual Wulst) of awake, behaving birds revealed a high proportion of neurons signaling such subjective contours, independent of local stimulus attributes. These data suggest that the visual Wulst is important in contour-based form perception and exhibits a functional complexity analogous to mammalian extrastriate cortex.
103 citations
Book•
01 Feb 1999
TL;DR: Note: 14incollection Reference LCN-CHAPTER-1998-002 URL: http://diwww.epfl.ch/~gerstner/PUBLICATIONS/PNN3.ps.Z Record created on 2006-12-12.
Abstract: Note: 14incollection Reference LCN-CHAPTER-1998-002 URL: http://diwww.epfl.ch/~gerstner/PUBLICATIONS/PNN3.ps.Z Record created on 2006-12-12, modified on 2017-05-12
54 citations
TL;DR: The early development of calretinin immunoreactivity (CR‐IR) was described in the auditory nuclei of the brainstem of the barn owl, and gradients moved along the future tonotopic axes during the development of all nuclei studied, until adult patterns of CR‐IR were achieved about a week after hatching.
Abstract: The early development of calretinin immunoreactivity (CR-IR) was described in the auditory nuclei of the brainstem of the barn owl. CR-IR was first observed in the auditory hindbrain at embryonic day (E17) and a day later (E18) in the inferior colliculus. In each of the auditory nuclei studied, CR-IR did not develop homogeneously, but began in the regions that map high best frequencies in the adult barn owl. In the hindbrain, CR-IR was first observed in the rostromedial regions of the cochlear nucleus magnocellularis and the nucleus laminaris, and in the dorsal regions of the nucleus angularis and in the nucleus of the lateral lemniscus. In the inferior colliculus, CR-IR began in the ventral region of the central core. The edge of these gradients moved along the future tonotopic axes during the development of all nuclei studied, until adult patterns of CR-IR were achieved about a week after hatching. J. Comp. Neurol. 415:189–203, 1999. © 1999 Wiley-Liss, Inc.
46 citations
TL;DR: In this paper, the authors showed that the absence of a dielectric β process in many glass-forming materials, e.g., salol (phenyl salicylate), is a matter of the slow cooling rates usually employed to enter the glassy state.
Abstract: The recently observed possibility to suppress the β-relaxation intensity of o-terphenyl by annealing at temperatures below the glass transition guided us to ask, whether the absence of a dielectric β process in many glass-forming materials, e.g., salol (phenyl salicylate), is a matter of the slow cooling rates usually employed to enter the glassy state. In order to assess this issue, we have quenched liquid salol to well below Tg at a rate of dT/dt=−490 K/min. Opposed to the case of cooling rates around −5 K/min or slower, this highly quenched sample displays a symmetric dielectric relaxation peak near f=103 Hz with an appreciable relaxation strength, Δe=6×10−3. This novel feature of salol disappears irreversibly after a temperature excursion towards the glass transition at Tg=220 K.
37 citations
TL;DR: In this article, the authors measured the electric modulus of the ionic conductor 0.4, 0.6, and 0.2, Ca(NO3)2-0.6 by recording the electric field relaxation E(t) under the constraints of a constant displacement D0.
Abstract: We have measured the electric modulus M(t) of the ionic conductor 0.4 Ca(NO3)2–0.6 KNO3 (CKN) by recording the electric field relaxation E(t) under the constraints of a constant displacement D0. The vitreous material CKN is studied in its glassy state for temperatures 240 K⩽T⩽330 K and for times 7×10−3 s⩽t⩽3×105 s. In this range the dc conductivity varies from 3×10−11 to 5×10−17 S/cm according to Arrhenius behavior. We show that the time dependent resistivity ρ(t), instead of the conductivity σ(t), is an appropriate quantity for assessing the time dependent and steady state effects of ionic diffusivity on the basis of experimental modulus data M(t) recorded in the time domain. Even substantial electrode polarization is not critical with regard to this data analysis.
33 citations
TL;DR: In this paper, the authors investigated the orientational behavior of a series of novel oligophenylenevinylenes which carry a sequence of hyperpolarizable and dipolar donor−acceptor (DA) pairs, designed to allow for a free rotation of the DA orientation in a plane perpendicular to the long molecular axis.
Abstract: We have investigated the orientational behavior of a series of novel oligophenylenevinylenes which carry a sequence of hyperpolarizable and dipolar donor−acceptor (DA) pairs, designed to allow for a free rotation of the DA orientation in a plane perpendicular to the long molecular axis. The studies include both the measurement of effective dipole moments, which are relevant for the degree of polar ordering required for second-harmonic generation, and the assessment of the time scales involved in the orientational motion of the effective dipole moment. The comparison between calculated dipole moments and those measured for different oligomers in toluene solution and in a polystyrene matrix confirm that a DA-pair separation of ≈10 A along the oligomer leads to a high chromophore concentration in the sample, yet without the unfavorable effect of aggregation or antiparallel alignment of neighboring dipole pairs. Both the bulkiness of the oligomer molecules and the electrostatic coupling of adjacent dipoles gi...
6 citations
01 Jan 1999
TL;DR: Note: incollection Reference LCN-CHAPTER-1999-001 URL: http://di.epfl.ch/~gerstner/PUBLICATIONS/badzw.ps.
Abstract: Note: incollection Reference LCN-CHAPTER-1999-001 URL: http://diwww.epfl.ch/~gerstner/PUBLICATIONS/badzw.ps.Z Record created on 2006-12-12, modified on 2017-05-12
1 citations