Identity of electrons and ionization equilibrium

It is perhaps appropriate that, in a year marking the 90th anniversary of Meghnad Saha seminal paper (1920), new developments should call fresh attention to the problem of ionization equilibrium in gases. Ionization equilibrium is considered in the simplest "physical" model for an electronic subsystem of matter in a rarefied state, consisting of one localized electronic state in each nucleus and delocalized electronic states considered as free ones. It is shown that, despite the qualitative agreement, there is a significant quantitative difference from the results of applying the Saha formula to the degree of ionization. This is caused by the fact that the Saha formula corresponds to the "chemical" model of matter.Comment: 9 pages, 2 figure

Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement

The dynamics of magnetization under femtosecond optical excitation is studied in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved magneto-optical Kerr effect measurement with two color probe beams. The transient reflectivity change indicates the rapid rise of the carrier temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a very slow rise of the spin temperature of the order of 500ps is observed. This anomalous behavior originates from the thermal isolation between the charge and spin systems due to the spin polarization of carriers (holes) contributing to ferromagnetism. This constitutes experimental proof of the half-metallic nature of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type mechanism originates from the d-band character of holes

Superdipole Liquid Scenario for the Dielectric Primary Relaxation in Supercooled Polar liquids

We propose a dynamic structure of coupled dynamic molecular strings for supercooled small polar molecule liquids and accordingly we obtain the Hamiltonian of the rotational degrees of freedom of the system. From the Hamiltonian, the strongly correlated supercooled polar liquid state is renormalized to a normal superdipole (SD) liquid state. This scenario describes the following main features of the primary or a-relaxation dynamics in supercooled polar liquids: (1) the average relaxation time evolves from a high temperature Arrhenius to a low temperature non-Arrhenius or super-Arrhenius behavior; (2) the relaxation function crosses over from the high temperature exponential to low temperature non-exponential form; and (3) the temperature dependence of the relaxation strength shows non-Curie features. According to the present model, the crossover phenomena of the first two characteristics arise from the transition between the superdipole gas and the superdipole liquid. The model predictions are quantitatively compared with the experimental results of glycerol, a typical glass-former.Comment: 40 pages, 3 figure

CaB_6: a new semiconducting material for spin electronics

Ferromagnetism was recently observed at unexpectedly high temperatures in La-doped CaB_6. The starting point of all theoretical proposals to explain this observation is a semimetallic electronic structure calculated for CaB_6 within the local density approximation. Here we report the results of parameter-free quasiparticle calculations of the single-particle excitation spectrum which show that CaB_6 is not a semimetal but a semiconductor with a band gap of 0.8 eV. Magnetism in La_xCa_{1-x}B_6 occurs just on the metallic side of a Mott transition in the La-induced impurity band.Comment: 4 pages, 1 postscript figur

Coordinated optimization of visual cortical maps (II) Numerical studies

It is an attractive hypothesis that the spatial structure of visual cortical architecture can be explained by the coordinated optimization of multiple visual cortical maps representing orientation preference (OP), ocular dominance (OD), spatial frequency, or direction preference. In part (I) of this study we defined a class of analytically tractable coordinated optimization models and solved representative examples in which a spatially complex organization of the orientation preference map is induced by inter-map interactions. We found that attractor solutions near symmetry breaking threshold predict a highly ordered map layout and require a substantial OD bias for OP pinwheel stabilization. Here we examine in numerical simulations whether such models exhibit biologically more realistic spatially irregular solutions at a finite distance from threshold and when transients towards attractor states are considered. We also examine whether model behavior qualitatively changes when the spatial periodicities of the two maps are detuned and when considering more than 2 feature dimensions. Our numerical results support the view that neither minimal energy states nor intermediate transient states of our coordinated optimization models successfully explain the spatially irregular architecture of the visual cortex. We discuss several alternative scenarios and additional factors that may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with arXiv:1102.335

Relevance theory, pragmatic inference and cognitive architecture

Relevance Theory (RT: Sperber & Wilson, 1986) argues that human language comprehension processes tend to maximize “relevance”, and postulates that there is a relevance-based procedure that a hearer follows when trying to understand an utterance. Despite being highly influential, RT has been criticized for its failure to explain how speaker-related information, either the speaker’s abilities or her/his preferences, is incorporated into the hearer’s inferential, pragmatic process. An alternative proposal is that speaker-related information gains prominence due to representation of the speaker within higher-level goal-directed schemata. Yet the goal-based account is still unable to explain clearly how cross-domain information, for example linguistic meaning and speaker-related knowledge, is integrated within a modular system. On the basis of RT’s cognitive requirements, together with contemporary cognitive theory, we argue that this integration is realized by utilizing working memory and that there exist conversational constraints with which the constructed utterance interpretation should be consistent. We illustrate our arguments with a computational implementation of the proposed processes within a general cognitive architecture

First report of generalized face processing difficulties in möbius sequence.

Reverse simulation models of facial expression recognition suggest that we recognize the emotions of others by running implicit motor programmes responsible for the production of that expression. Previous work has tested this theory by examining facial expression recognition in participants with Möbius sequence, a condition characterized by congenital bilateral facial paralysis. However, a mixed pattern of findings has emerged, and it has not yet been tested whether these individuals can imagine facial expressions, a process also hypothesized to be underpinned by proprioceptive feedback from the face. We investigated this issue by examining expression recognition and imagery in six participants with Möbius sequence, and also carried out tests assessing facial identity and object recognition, as well as basic visual processing. While five of the six participants presented with expression recognition impairments, only one was impaired at the imagery of facial expressions. Further, five participants presented with other difficulties in the recognition of facial identity or objects, or in lower-level visual processing. We discuss the implications of our findings for the reverse simulation model, and suggest that facial identity recognition impairments may be more severe in the condition than has previously been noted

You turn me cold: evidence for temperature contagion

Introduction During social interactions, our own physiological responses influence those of others. Synchronization of physiological (and behavioural) responses can facilitate emotional understanding and group coherence through inter-subjectivity. Here we investigate if observing cues indicating a change in another's body temperature results in a corresponding temperature change in the observer. Methods Thirty-six healthy participants (age; 22.9±3.1 yrs) each observed, then rated, eight purpose-made videos (3 min duration) that depicted actors with either their right or left hand in visibly warm (warm videos) or cold water (cold videos). Four control videos with the actors' hand in front of the water were also shown. Temperature of participant observers' right and left hands was concurrently measured using a thermistor within a Wheatstone bridge with a theoretical temperature sensitivity of <0.0001°C. Temperature data were analysed in a repeated measures ANOVA (temperature × actor's hand × observer's hand). Results Participants rated the videos showing hands immersed in cold water as being significantly cooler than hands immersed in warm water, F(1,34) = 256.67, p0.1). There was however no evidence of left-right mirroring of these temperature effects p>0.1). Sensitivity to temperature contagion was also predicted by inter-individual differences in self-report empathy. Conclusions We illustrate physiological contagion of temperature in healthy individuals, suggesting that empathetic understanding for primary low-level physiological challenges (as well as more complex emotions) are grounded in somatic simulation