Pure pairs. I. Trees and linear anticomplete pairs

The Erdos-Hajnal Conjecture asserts that for every graph H there is a constant c > 0 such that every graph G that does not contain H as an induced subgraph has a clique or stable set of cardinality at least |G|^c. In this paper, we prove a conjecture of Liebenau and Pilipczuk, that for every forest H there exists c > 0, such that every graph G contains either an induced copy of H, or a vertex of degree at least c|G|, or two disjoint sets of at least c|G| vertices with no edges between them. It follows that for every forest H there is c > 0 so that if G contains neither H nor its complement as an induced subgraph then there is a clique or stable set of cardinality at least |G|^c

Perceptual centres in speech - an acoustic analysis.

Perceptual centres, or P-centres, represent the perceptual moments of occurrence of acoustic signals - the 'beat' of a sound. P-centres underlie the perception and production of rhythm in perceptually regular speech sequences. P-centres have been modelled both in speech and non speech (music) domains. The three aims of this thesis were toatest out current P-centre models to determine which best accounted for the experimental data bto identify a candidate parameter to map P-centres onto (a local approach) as opposed to the previous global models which rely upon the whole signal to determine the P-centre the final aim was to develop a model of P-centre location which could be applied to speech and non speech signals. The first aim was investigated by a series of experiments in which a) speech from different speakers was investigated to determine whether different models could account for variation between speakers b) whether rendering the amplitude time plot of a speech signal affects the P-centre of the signal c) whether increasing the amplitude at the offset of a speech signal alters P-centres in the production and perception of speech. The second aim was carried out by a) manipulating the rise time of different speech signals to determine whether the P-centre was affected, and whether the type of speech sound ramped affected the P-centre shift b) manipulating the rise time and decay time of a synthetic vowel to determine whether the onset alteration was had more affect on P-centre than the offset manipulation c) and whether the duration of a vowel affected the P-centre, if other attributes (amplitude, spectral contents) were held constant. The third aim - modelling P-centres - was based on these results. The Frequency dependent Amplitude Increase Model of P-centre location (FAIM) was developed using a modelling protocol, the APU GammaTone Filterbank and the speech from different speakers. The P-centres of the stimuli corpus were highly predicted by attributes of the increase in amplitude within one output channel of the filterbank. When this was used to make predictions of the P-centres for all the stimuli used in the thesis, 85[percent] of the observed variance was accounted for. The FAIM approach combines aspects of previous, speech and non speech models (Gordon 1987, Marcus 1981, Vos and Rasch 1981). P-centre were thus modelled in a non speech specific, local manner

Amplitude Onsets and Spectral Energy in Perceptual Experience

A commentary on A temporal sampling framework for developmental dyslexi

The properties of molecular ions

This thesis presents the results of a series of experimental investigations of the single and double ionization of atmospheric molecules. In particular, the formation and dissociation of singly and doubly charged molecular ions are studied using electron-impact time-of-flight mass spectrometry and ion-ion coincidence techniques. The target atmospheric molecules under investigation are dinitrogen pentoxide (N2O5), nitric acid (HNO3), chlorine dioxide (OCIO) and chlorine monoxide (CI2O). These molecules are thought to play significant roles in the atmospheric ozone cycle as the sources of ozone-destroying radicals. However, despite the potential atmospheric importance of these reactive molecules and the interest in their photodissociation and spectroscopic properties, there have been relatively few investigations of their ionization. In the single ionization studies, electron-impact time-of-flight mass spectrometry is used to determine the relative partial single ionization cross sections of the ions produced upon single ionization of the target molecules from near threshold to 500 eV. In the case of N2O5 and HNO3, the appearance energies of previously unobserved fragment ions are also reported. The first investigations of the double ionization of the target species are also reported in this thesis. In order to study the formation and fragmentation of the doubly charged molecular ions (dications), ion-ion coincidence techniques coupled with time-of-flight mass spectrometry have been developed. One and two-dimensional coincidence experiments have been performed, where the distinction between these experiments arises from the dimensionality of the data set recorded. In the one-dimensional experiments, comparisons of the experimentally determined appearance energies for the dication dissociation reactions with the energetics derived from the kinetic energy release involved in these dissociation processes give (i) an indication of the mechanisms by which the doubly-charged molecules dissociate and (ii) the energy of the dication electronic states which are the source of the fragment ions. From the 2D coincidence spectra, analysis of the ion pair intensities and peak slopes can also be inteipreted to yield information concerning dication dissociation mechanisms. These investigations have led to the first evaluation of the ratio of double-to-single ionization cross sections for CI2O, OCIO and HNO3. In addition, first estimates of the double ionization energy of N2O5, HNO3, OCIO and CI2O and the development of the first models of their decay dynamics have also been made

Bromostibine complexes of iron(II): hypervalency and reactivity

The halostibine complexes [CpFe(CO)2(SbMe2Br)][CF3SO3] and [CpFe(CO)2(SbMe2Br)][BF4] both contain significant interactions between the anion and the formally neutral Sb(III) ligand, which simultaneously displays Lewis acidic and Lewis basic properties. The unexpected secondary product [CpFe(CO)(Me2BrSb-?-Br-SbBrMe2)] is formed in the presence of excess ligand, the strongly associated Br– anion bridging the two Sb donors to form a four-membered FeSb2Br ring.<br/

Voluntary and involuntary processes affect the production of verbal and non-verbal signals by the human voice.

AbstractWe argue that a comprehensive model of human vocal behaviour must address both voluntary and involuntary aspects of articulate speech and non-verbal vocalizations. Within this, plasticity of vocal output should be acknowledged and explained as part of the mature speech production system.</jats:p

Rostro-caudal networks for sound processing in the primate brain

Sound is processed in primate brains along anatomically and functionally distinct streams: this pattern can be seen in both human and non-human primates. We have previously proposed a general auditory processing framework in which these different perceptual profiles are associated with different computational characteristics. In this paper we consider how recent work supports our framework

Suppressing sensorimotor activity modulates the discrimination of auditory emotions but not speaker identity

Our ability to recognize the emotions of others is a crucial feature of human social cognition. Functional neuroimaging studies indicate that activity in sensorimotor cortices is evoked during the perception of emotion. In the visual domain, right somatosensory cortex activity has been shown to be critical for facial emotion recognition. However, the importance of sensorimotor representations in modalities outside of vision remains unknown. Here we use continuous theta-burst transcranial magnetic stimulation (cTBS) to investigate whether neural activity in the right postcentral gyrus (rPoG) and right lateral premotor cortex (rPM) is involved in nonverbal auditory emotion recognition. Three groups of participants completed same-different tasks on auditory stimuli, discriminating between the emotion expressed and the speakers' identities, before and following cTBS targeted at rPoG, rPM, or the vertex (control site). A task-selective deficit in auditory emotion discrimination was observed. Stimulation to rPoG and rPM resulted in a disruption of participants' abilities to discriminate emotion, but not identity, from vocal signals. These findings suggest that sensorimotor activity may be a modality-independent mechanism which aids emotion discrimination. Copyright © 2010 the authors