| 1. |
- Asenjo, Felipe A., et al.
(författare)
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Semi-relativistic effects in spin-1/2 quantum plasmas
- 2012
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14, s. 073042-
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Tidskriftsartikel (refereegranskat)abstract
- Emerging possibilities for creating and studying novel plasma regimes, e. g. relativistic plasmas and dense systems, in a controlled laboratory environment also require new modeling tools for such systems. This motivates theoretical studies of the kinetic theory governing the dynamics of plasmas for which both relativistic and quantum effects occur simultaneously. Here, we investigate relativistic corrections to the Pauli Hamiltonian in the context of a scalar kinetic theory for spin-1/2 quantum plasmas. In particular, we formulate a quantum kinetic theory for the collective motion of electrons that takes into account effects such as spin-orbit coupling and Zitterbewegung. We discuss the implications and possible applications of our findings.
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| 2. |
- de Frias, Cindy M., et al.
(författare)
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Influence of COMT Gene Polymorphism on fMRI-assessed Sustained and Transient Activity during a Working Memory Task
- 2010
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Ingår i: Journal of cognitive neuroscience. - Cambridge, Mass. : MIT Press. - 0898-929X .- 1530-8898. ; 22:7, s. 1614-1622
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Tidskriftsartikel (refereegranskat)abstract
- The catechol O-methyltransferase (COMT) gene-encoding an enzyme that is essential for the degradation of dopamine (DA) in prefrontal cortex (PFC)-contains a single nucleotide polymorphism (val/met) important for cognition. According to the tonic-phasic hypothesis, individuals carrying the low-enzyme- activity allele (met) are characterized by enhanced tonic DA activity in PFC, promoting sustained cognitive representations in working memory. Val carriers have reduced tonic but enhanced phasic dopaminergic activity in subcortical regions, enhancing cognitive flexibility. We tested the tonic-phasic DA hypothesis by dissociating sustained and transient brain activity during performance on a 2-back working memory test using mixed blocked/event-related functional magnetic resonance imaging. Participants were men recruited from a random sample of the population (the Betula study) and consisted of 11 met/met and 11 val/val carriers aged 50 to 65 years, matched on age, education, and cognitive performance. There were no differences in 2-back performance between genotype groups. Met carriers displayed a greater transient medial temporal lobe response in the updating phase of working memory, whereas val carriers showed a greater sustained PFC activation in the maintenance phase. These results support the tonic-phasic theory of DA function in elucidating the specific phenotypic influence of the COMT val(158)met polymorphism on different components of working memory.
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| 3. |
- Edlund, Jens, et al.
(författare)
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3rd party observer gaze as a continuous measure of dialogue flow
- 2012
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Ingår i: Proceedings of the 8th International Conference on Language Resources and Evaluation, LREC 2012. - Istanbul, Turkey : LREC. ; , s. 1354-1358
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Konferensbidrag (refereegranskat)abstract
- We present an attempt at using 3rd party observer gaze to get a measure of how appropriate each segment in a dialogue is for a speaker change. The method is a step away from the current dependency of speaker turns or talkspurts towards a more general view of speaker changes. We show that 3rd party observers do indeed largely look at the same thing (the speaker), and how this can be captured and utilized to provide insights into human communication. In addition, the results also suggest that there might be differences in the distribution of 3rd party observer gaze depending on how information-rich an utterance is.
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| 4. |
- Hammar, Petter, et al.
(författare)
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The lac repressor displays facilitated diffusion in living cells
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 336:6088, s. 1595-1598
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Tidskriftsartikel (refereegranskat)abstract
- Transcription factors (TFs) are proteins that regulate the expression of genes by binding sequence-specific sites on the chromosome. It has been proposed that to find these sites fast and accurately, TFs combine one-dimensional (1D) sliding on DNA with 3D diffusion in the cytoplasm. This facilitated diffusion mechanism has been demonstrated in vitro, but it has not been shown experimentally to be exploited in living cells. We have developed a single-molecule assay that allows us to investigate the sliding process in living bacteria. Here we show that the lac repressor slides 45 ± 10 base pairs on chromosomal DNA and that sliding can be obstructed by other DNA-bound proteins near the operator. Furthermore, the repressor frequently (>90%) slides over its natural lacO(1) operator several times before binding. This suggests a trade-off between rapid search on nonspecific sequences and fast binding at the specific sequence.
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| 5. |
- Ilderton, Anton, et al.
(författare)
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Pair annihilation in laser pulses : Optical versus x-ray free-electron laser regimes
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - New York, N.Y. : Publ. by the American Physical Society through the American Institute of Physics. - 1050-2947 .- 1094-1622. ; 84:3, s. 032119-
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the theory and phenomenology of pair annihilation, within an ultrashort laser pulse, to a single photon. The signature of this process is the unidirectional emission of single photons with a fixed energy. We show that the cross section is significantly larger than for two-photon pair annihilation in vacuum, with x-ray free-electron laser parameters admitting a much clearer signal than optical beams.
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| 6. |
- Klintfors, Eeva, et al.
(författare)
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Cortical N400-potentials generated by adults in response to semantic incongruities
- 2011
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Ingår i: Proceedings of Fonetik 2011. - Stockholm, Sweden : Universitetsserveice AB. ; , s. 121-124
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Eight adult participants were investigated in a pre-experiment for the future assessment of semantic N400 effects in children. The materials were words resented in semantically incongruent vs. congruent picture contexts. For example, he word duck was played while a picture of a tree was shown in the incongruent est condition vs. the word duck was played while a picture of a duck was shown in the congruent test condition. A larger N400 effect was expected in response to the incongruent audio-visual pairings. The results showed in time extended peak-to peak differences between congruent and incongruent audio-visual pairings at the centroparietal, parietal and parieto-occipital recording sites. This study was performed to validate the current materials to be used to answer questions on appearance of the N400 component in children.
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| 7. |
- Lansner, Anders, et al.
(författare)
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Reactivation in Working Memory : An Attractor Network Model of Free Recall
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:8, s. e73776-
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic nature of human working memory, the general-purpose system for processing continuous input, while keeping no longer externally available information active in the background, is well captured in immediate free recall of supraspan word-lists. Free recall tasks produce several benchmark memory phenomena, like the U-shaped serial position curve, reflecting enhanced memory for early and late list items. To account for empirical data, including primacy and recency as well as contiguity effects, we propose here a neurobiologically based neural network model that unifies short- and long-term forms of memory and challenges both the standard view of working memory as persistent activity and dual-store accounts of free recall. Rapidly expressed and volatile synaptic plasticity, modulated intrinsic excitability, and spike-frequency adaptation are suggested as key cellular mechanisms underlying working memory encoding, reactivation and recall. Recent findings on the synaptic and molecular mechanisms behind early LTP and on spiking activity during delayed-match-to-sample tasks support this view.
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| 8. |
- Marklund, Erik G., et al.
(författare)
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Transcription-factor binding and sliding on DNA studied using micro- and macroscopic models
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:49, s. 19796-19801
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Tidskriftsartikel (refereegranskat)abstract
- Transcription factors search for specific operator sequences by alternating rounds of 3D diffusion with rounds of 1D diffusion (sliding) along the DNA. The details of such sliding have largely been beyond direct experimental observation. For this purpose we devised an analytical formulation of umbrella sampling along a helical coordinate, and from extensive and fully atomistic simulations we quantified the free-energy landscapes that underlie the sliding dynamics and dissociation kinetics for the LacI dimer. The resulting potential of mean force distributions show a fine structure with an amplitude of 1 k(B)T for sliding and 12 kBT for dissociation. Based on the free-energy calculations the repressor slides in close contact with DNA for 8 bp on average before making a microscopic dissociation. By combining the microscopic molecular-dynamics calculations with Brownian simulation including rotational diffusion from the microscopically dissociated state we estimate a macroscopic residence time of 48 ms at the same DNA segment and an in vitro sliding distance of 240 bp. The sliding distance is in agreement with previous in vitro sliding-length estimates. The in vitro prediction for the macroscopic residence time also compares favorably to what we measure by single-molecule imaging of nonspecifically bound fluorescently labeled LacI in living cells. The investigation adds to our understanding of transcription-factor search kinetics and connects the macro-/mesoscopic rate constants to the microscopic dynamics.
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| 9. |
- Marklund, Petter, et al.
(författare)
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Context dependent switching between proactive and reactive working memory control mechanisms in the right inferior frontal gyrus
- 2012
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 63:3, s. 1552-1560
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Tidskriftsartikel (refereegranskat)abstract
- A critical feature of higher cognitive functioning is the capacity to flexibly tailor information processing and behaviors to current situational demands. Recent neurocognitive models have been postulated to account for the dynamic nature of human executive processing by invoking two dissociable cognitive control modes, proactive and reactive control. These may involve partially overlapping, but temporally distinct neural implementation in the prefrontal cortex. Prior brain imaging studies exploring proactive control have mainly used tasks requiring only information about single-items to be retained over unfilled delays. Whether proactive control can also be utilized to facilitate performance in more complex working memory tasks, in which concurrent processing of intervening items and updating is mandatory during contextual cue maintenance remains an open question. To examine this issue and to elucidate the extent to which overlapping neural substrates underlie proactive and reactive control we used fMRI and a modified verbal 3-back paradigm with embedded cues predictive of high-interference trials. This task requires context information to be retained over multiple intervening trials. We found that performance improved with item-specific cues predicting forthcoming lures despite increased working memory load. Temporal dynamics of activation in the right inferior frontal gyrus suggest flexible switching between proactive and reactive control in a context-dependent fashion, with greater sustained responses elicited in the 3-back task involving context maintenance of cue information and greater transient responses elicited in the 3-back task absent of cues.
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| 10. |
- Stenfors, Cecilia U. D., et al.
(författare)
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Subjective Cognitive Complaints and the Role of Executive Cognitive Functioning in the Working Population : A Case-Control Study
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:12, s. UNSP e83351-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Cognitive functioning is important for managing work and life in general. However, subjective cognitive complaints (SCC), involving perceived difficulties with concentration, memory, decision making, and clear thinking are common in the general and working population and can be coupled with both lowered well-being and work ability. However, the relation between SCC and cognitive functioning across the adult age-span, and in the work force, is not clear as few population-based studies have been conducted on non-elderly adults. Thus, the present study aimed to test the relation between SCC and executive cognitive functioning in a population-based sample of employees. Methods: Participants were 233 employees with either high (cases) or low (controls) levels of SCC. Group differences in neuropsychological test performance on three common executive cognitive tests were analysed through a set of analyses of covariance tests, including relevant covariates. Results & Conclusions: In line with the a priori hypotheses, a high level of SCC was associated with significantly poorer executive cognitive performance on all three executive cognitive tests used, compared to controls with little SCC. Additionally, symptoms of depression, chronic stress and sleeping problems were found to play a role in the relations between SCC and executive cognitive functioning. No significant associations remained after adjusting for all these factors. The current findings contribute to an increased understanding of what characterizes SCC in the work force and may be used at different levels of prevention of- and intervention for SCC and related problems with executive cognitive functioning.
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