541 research outputs found
Excitations and benchmark ensemble density functional theory for two electrons
A new method for extracting ensemble Kohn-Sham potentials from accurate
excited state densities is applied to a variety of two electron systems,
exploring the behavior of exact ensemble density functional theory. The issue
of separating the Hartree energy and the choice of degenerate eigenstates is
explored. A new approximation, spin eigenstate Hartree-exchange (SEHX), is
derived. Exact conditions that are proven include the signs of the correlation
energy components, the virial theorem for both exchange and correlation, and
the asymptotic behavior of the potential for small weights of the excited
states. Many energy components are given as a function of the weights for two
electrons in a one-dimensional flat box, in a box with a large barrier to
create charge transfer excitations, in a three-dimensional harmonic well
(Hooke's atom), and for the He atom singlet-triplet ensemble,
singlet-triplet-singlet ensemble, and triplet bi-ensemble.Comment: 15 pages, supplemental material pd
Dissipation and spontaneous symmetry breaking in brain dynamics
We compare the predictions of the dissipative quantum model of brain with
neurophysiological data collected from electroencephalograms resulting from
high-density arrays fixed on the surfaces of primary sensory and limbic areas
of trained rabbits and cats. Functional brain imaging in relation to behavior
reveals the formation of coherent domains of synchronized neuronal oscillatory
activity and phase transitions predicted by the dissipative model.Comment: Restyled, slight changes in title and abstract, updated bibliography,
J. Phys. A: Math. Theor. Vol. 41 (2008) in prin
Synthetic Quantum Systems
So far proposed quantum computers use fragile and environmentally sensitive
natural quantum systems. Here we explore the new notion that synthetic quantum
systems suitable for quantum computation may be fabricated from smart
nanostructures using topological excitations of a stochastic neural-type
network that can mimic natural quantum systems. These developments are a
technological application of process physics which is an information theory of
reality in which space and quantum phenomena are emergent, and so indicates the
deep origins of quantum phenomena. Analogous complex stochastic dynamical
systems have recently been proposed within neurobiology to deal with the
emergent complexity of biosystems, particularly the biodynamics of higher brain
function. The reasons for analogous discoveries in fundamental physics and
neurobiology are discussed.Comment: 16 pages, Latex, 1 eps figure fil
P300 and uncertainty reduction in a concept identification task.
The relationship between the amplitude of P300, the mean amplitude of the Slow Wave, and uncertainty reduction after (dis)confirmation of hypotheses was studied in a Concept-Identification task. The subjects had to categorize stimuli according to a conceptual rule (joint denial or exclusion) and to rate the confidence that their classification was correct. Three types of feedback were distinguished: confirming (subject's categorization was correct), disconfirming (subject's categorization was incorrect), and non-informative feedback. The EEG was averaged separately according to the three types of feedback and the two confidence ratings (low, high).
The data showed the predicted interaction between type of feedback and confidence level. A larger P300 amplitude turned up after confirming feedback when the subject was less confident, than when he was more confident. The reverse was found after disconfirming feedback. The P300 amplitude after non-informative feedback was not influenced by confidence. The mean amplitude of the Slow Wave showed approximately the same interaction pattern.
The results were interpreted in terms of changes in the probability of hypotheses which subjects use to categorize stimuli in a Concept-Identification task
Variability in the articulation and perception of a word
The words making up a speaker’s mental lexicon may be stored as abstract phonological representations or else they may be stored as detailed acoustic-phonetic representations. The speaker’s articulatory gestures intended to represent a word show relatively high variability in spontaneous speech. The aim of this paper is to explore the acoustic-phonetic patterns of the Hungarian word
akkor
‘then, at that time’. Ten speakers’ recorded spontaneous speech with a total duration of 255 minutes and containing 286 occurrences of akkor were submitted to analysis. Durational and frequency patterns were measured by means of the Praat software. The results obtained show higher variability both within and across speakers than it had been expected. Both the durations of the words and those of the speech sounds, as well as the vowel formants, turned out to significantly differ across speakers. In addition, the results showed considerable within-speaker variation as well. The correspondence between variability in the objective acoustic-phonetic data and the flexibility and adaptive nature of the mental representation of a word will be discussed.For the perception experiments, two speakers of the previous experiment were selected whose 48 words were then used as speech material. The listeners had to judge the quality of the words they heard using a five-point scale. The results confirmed that the listeners used diverse strategies and representations depending on the acoustic-phonetic parameters of the series of occurrences of
akkor
The role of conviction and narrative in decision-making under radical uncertainty
We propose conviction narrative theory (CNT) to broaden decision-making theory for it better to understand and analyse how subjectively means-end rational actors cope in contexts in which the traditional assumptions in decision-making models fail to hold. Conviction narratives enable actors to draw on their beliefs, causal models and rules of thumb to identify opportunities worth acting on, to simulate the future outcome of their actions and to feel sufficiently convinced to act. The framework focuses on how narrative and emotion combine to allow actors to deliberate and to select actions that they think will produce the outcomes they desire. It specifies connections between particular emotions and deliberative thought, hypothesizing that approach and avoidance emotions evoked during narrative simulation play a crucial role. Two mental states, Divided and Integrated, in which narratives can be formed or updated, are introduced and used to explain some familiar problems that traditional models cannot
The “conscious pilot”—dendritic synchrony moves through the brain to mediate consciousness
Cognitive brain functions including sensory processing and control of behavior are understood as “neurocomputation” in axonal–dendritic synaptic networks of “integrate-and-fire” neurons. Cognitive neurocomputation with consciousness is accompanied by 30- to 90-Hz gamma synchrony electroencephalography (EEG), and non-conscious neurocomputation is not. Gamma synchrony EEG derives largely from neuronal groups linked by dendritic–dendritic gap junctions, forming transient syncytia (“dendritic webs”) in input/integration layers oriented sideways to axonal–dendritic neurocomputational flow. As gap junctions open and close, a gamma-synchronized dendritic web can rapidly change topology and move through the brain as a spatiotemporal envelope performing collective integration and volitional choices correlating with consciousness. The “conscious pilot” is a metaphorical description for a mobile gamma-synchronized dendritic web as vehicle for a conscious agent/pilot which experiences and assumes control of otherwise non-conscious auto-pilot neurocomputation
Melting a Hubbard dimer: benchmarks of 'ALDA' for quantum thermodynamics
The competition between evolution time, interaction strength, and temperature
challenges our understanding of many-body quantum systems out-of-equilibrium.
Here we consider a benchmark system, the Hubbard dimer, which allows us to
explore all the relevant regimes and calculate exactly the related average
quantum work. At difference with previous studies, we focus on the effect of
increasing temperature, and show how this can turn competition between
many-body interactions and driving field into synergy. We then turn to use
recently proposed protocols inspired by density functional theory to explore if
these effects could be reproduced by using simple approximations. We find that,
up to and including intermediate temperatures, a method which borrows from
ground-state adiabatic local density approximation improves dramatically the
estimate for the average quantum work, including, in the adiabatic regime, when
correlations are strong. However at high temperature and at least when based on
the pseudo-LDA, this method fails to capture the counterintuitive qualitative
dependence of the quantum work with interaction strength, albeit getting the
quantitative estimates relatively close to the exact results
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