Charge density wave in graphene: magnetic-field-induced Peierls instability

We suggest that a magnetic-field-induced Peierls instability accounts for the recent experiment of Zhang et al. in which unexpected quantum Hall plateaus were observed at high magnetic fields in graphene on a substrate. This Peierls instability leads to an out-of-plane lattice distortion resulting in a charge density wave (CDW) on sublattices A and B of the graphene honeycomb lattice. We also discuss alternative microscopic scenarios proposed in the literature and leading to a similar CDW ground state in graphene.Comment: Proceeding of the "graphene conference" (25 September - 01 October 2006) held in Dresde

The influence of the palate shape on articulatory token-to-token variability

Articulatory token-to-token variability not only depends on linguistic aspects like the phoneme inventory of a given language but also on speaker specific morphological and motor constraints. As has been noted previously (Perkell (1997), Mooshammer et al. (2004)) , speakers with coronally high "domeshaped" palates exhibit more articulatory variability than speakers with coronally low "flat" palates. One explanation for that is based on perception oriented control by the speaker. The influence of articulatory variation on the cross sectional area and consequently on the acoustics should be greater for flat palates than for domeshaped ones. This should force speakers with flat palates to place their tongue very precisely whereas speakers with domeshaped palates might tolerate a greater variability. A second explanation could be a greater amount of lateral linguo-palatal contact for flat palates holding the tongue in position. In this study both hypotheses were tested

Temporal development of compensation strategies for perturbed palate shape in German /S/-production

The palate shape of four speakers was changed by a prosthesis which either lowered the palate or retracted the alveoles. Subjects wore the prosthesis for two weeks and were recorded several times via EMA. Results of articulatory measurements show that speakers use different compensation methods at different stages of the adaptation. They lower the tongue immediately after the insertion of the prosthesis. Other compensation methods as for example lip protrusion are only acquired after longer practising periods. The results are interpreted as supporting the existence of different mappings between motor commands, vocal tract shape and auditory-acoustic target

Spontaneous parity breaking of graphene in the quantum Hall regime

We propose that the inversion symmetry of the graphene honeycomb lattice is spontaneously broken via a magnetic field dependent Peierls distortion. This leads to valley splitting of the $n=0$ Landau level but not of the other Landau levels. Compared to quantum Hall valley ferromagnetism recently discussed in the literature, lattice distortion provides an alternative explanation to all the currently observed quantum Hall plateaus in graphene.Comment: 4 pages, to appear in Phys. Rev. Let

Motor Equivalence in Speech Production

International audienceThe first section provides a description of the concepts of “motor equivalence” and “degrees of freedom”. It is illustrated with a few examples of motor tasks in general and of speech production tasks in particular. In the second section, the methodology used to investigate experimentally motor equivalence phenomena in speech production is presented. It is mainly based on paradigms that perturb the perception-action loop during on-going speech, either by limiting the degrees of freedom of the speech motor system, or by changing the physical conditions of speech production or by modifying the feedback information. Examples are provided for each of these approaches. Implications of these studies for a better understanding of speech production and its interactions with speech perception are presented in the last section. Implications are mainly related to characterization of the mechanisms underlying interarticulatory coordination and to the analysis of the speech production goals

Motor Equivalence in Speech Production

International audienceThe first section provides a description of the concepts of “motor equivalence” and “degrees of freedom”. It is illustrated with a few examples of motor tasks in general and of speech production tasks in particular. In the second section, the methodology used to investigate experimentally motor equivalence phenomena in speech production is presented. It is mainly based on paradigms that perturb the perception-action loop during on-going speech, either by limiting the degrees of freedom of the speech motor system, or by changing the physical conditions of speech production or by modifying the feedback information. Examples are provided for each of these approaches. Implications of these studies for a better understanding of speech production and its interactions with speech perception are presented in the last section. Implications are mainly related to characterization of the mechanisms underlying interarticulatory coordination and to the analysis of the speech production goals

Combinatorial models for topology-based geometric modeling

Many combinatorial (topological) models have been proposed in geometric modeling, computational geometry, image processing or analysis, for representing subdivided geometric objects, i.e. partitionned into cells of different dimensions: vertices, edges, faces, volumes, etc. We can distinguish among models according to the type of cells (regular or not regular ones), the type of assembly ("manifold" or "non manifold"), the type of representation (incidence graphs or ordered models), etc

Influence de la forme du palais sur la variabilité articulatoire

As has been noted previously, speakers with coronally low "flat" palates exhibit less articulatory variability than speakers with coronally high "domeshaped" palates. This phenomenon is investigated by means of a tongue model and an EPG experiment. The results show that acoustic variability depends on the shape of the vocal tract. The same articulatory variability leads to more acoustic variability if the palate is flat than if it is domeshaped. Furthermore, speakers with domeshaped palates show more articulatory variability than speakers with flat palates. The results are explained by different control strategies by the speakers. Speakers with flat palates reduce their articulatory variability in order to keep their acoustic variability low

Supralaryngeal control in Korean velar stops

International audienceThe aim of this study was to investigate the supralaryngeal control of the production of the Korean three-way contrast in velar stops. First, an EMA-experiment with three Korean speakers was carried out, and the kinematic properties of the tongue back were analyzed (length of the deceleration phase of the movement, peak velocity, peak acceleration, amplitude and duration of the looping movement during consonantal closure, and angle of incidence between tongue and palate at contact onset). To understand the potential motor control mechanisms underlying the production of the three-way contrast, the target hypothesis which suggests that articulator movements in stops are directed towards a target at or beyond the palate, was evaluated by comparing its predictions with our experimental findings. Evidence was found in support of this hypothesis. Hence, the hypothesis was further explored in a modeling study. The results suggest that variability in the articulatory parameters can be explained by a single control parameter, namely the target position of the tongue. In a third step the Korean velar stops were simulated by varying the target position. The results show that the main trends of the simulated consonants are in good agreement with the experimental findings

On the relationship between palate shape and articulatory behavior

International audienceIn this study the acoustic and articulatory variability of speakers with different palate shapes were compared. Since the cross-sectional area of the vocal tract changes less for a slight change in tongue position if the palate is domeshaped than if it is flat, the acoustic variability should be greater for flat palates than for domeshaped ones. Consequently, it can be hypothesized that speakers with flat palates should reduce their articulatory variability in order to keep the acoustic output constant. This hypothesis was tested on 32 speakers recorded via EPG and acoustics. The articulatory and acoustic variability of some of their vowels and /j/ was measured. Indeed, the results show that the speakers with flat palates reduce their variability in tongue height. There is no such trend in acoustic variability