89 research outputs found

    Chaos and Thermalization in the one-dimensional Bose-Hubbard model in the classical-field approximation

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    In this thesis, we present a comprehensive study of chaos and thermalization of the one-dimensional Bose-Hubbard Model (BHM) within the classical field approximation. Two quantitative measures are compared: the ensemble-averaged Finite-time Maximal Lyapunov exponent, a measures of chaos and the normalized spectral entropy, a measure of the distance between the numerical time-averaged momentum distribution and the one predicted by thermodynamics. A threshold for chaos is found, which depends on two parameters, the nonlinearity and the total energy-per-particle. Below the threshold, the dynamics are regular, while far above the threshold, complete thermalization is observed, as measured by the normalized spectral entropy. We study individual resonances in the Bose-Hubbard model to determine the criterion for chaos. The criterion based on Chirikov's method of overlapping resonances diverges in the thermodynamic limit, in contrast to the criterion parameters inferred from numerical calculations, signifying the failure of the standard Chirikov's approach. The Ablowitz-Ladik lattice is one of several integrable models that are close to the BHM. We outline the method of Inverse Scattering Transform and generate the integrals of motion of the Ablowitz-Ladik lattice. Furthermore, we discuss the possible role of these quantities in the relaxation dynamics of the BHM.Comment: PhD Thesis. 143 pages. Minor edits

    Generalized Thermalization in an Integrable Lattice System

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    After a quench, observables in an integrable system may not relax to the standard thermal values, but can relax to the ones predicted by the generalized Gibbs ensemble (GGE) [M. Rigol et al., Phys. Rev. Lett. 98, 050405 (2007)]. The GGE has been shown to accurately describe observables in various one-dimensional integrable systems, but the origin of its success is not fully understood. Here we introduce a microcanonical version of the GGE and provide a justification of the GGE based on a generalized interpretation of the eigenstate thermalization hypothesis, which was previously introduced to explain thermalization of nonintegrable systems. We study relaxation after a quench of one-dimensional hard-core bosons in an optical lattice. Exact numerical calculations for up to 10 particles on 50 lattice sites (~10^10 eigenstates) validate our approach.Comment: 8 pages, 9 figures, as publishe

    Threshold for Chaos and Thermalization in One-Dimensional Mean-Field Bose-Hubbard Model

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    We study the threshold for chaos and its relation to thermalization in the 1D mean-field Bose-Hubbard model, which in particular describes atoms in optical lattices. We identify the threshold for chaos, which is finite in the thermodynamic limit, and show that it is indeed a precursor of thermalization. Far above the threshold, the state of the system after relaxation is governed by the usual laws of statistical mechanics.Comment: 4 pages, 3 figures, published versio

    Impact of a Reduced Nicotine Standard on Young Adult Appeal for Menthol and Non-Menthol Cigarettes

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    Introduction The Food and Drug Administration (FDA) announced its intention to reduce the nicotine content in cigarettes as a strategy to promote cessation and reduce smoking-related harm. A low nicotine product standard will apply to all cigarettes on the market, including menthol cigarettes. In December 2021, the FDA approved a modified risk tobacco product application for menthol and non-menthol flavoured very low nicotine cigarettes (VLNC) from the 22nd Century Group. Notably, experimentation with menthol cigarettes is linked to smoking progression, as well as greater nicotine dependence relative to non-menthol cigarette use. If menthol VLNCs are perceived as more appealing than non-menthol VLNCs, this would indicate that some aspect of menthol may maintain smoking even in the absence of nicotine and FDA’s regulatory authority to ban or restrict the sale of menthol cigarettes should apply to reduced nicotine content of cigarettes. In April 2022, the FDA announced proposed rulemaking to prohibit menthol cigarettes, however it is unclear if a menthol prohibition would apply to VLNCs. Methods and analysis This study will recruit 172 young adult menthol smokers (with a specific subsample of n=40 sexual and gender minority young adults) and measure appeal for smoking experimental menthol and non-menthol VLNCs, and the impact of proposed product standards on tobacco product purchasing behaviour using an Experimental Tobacco Marketplace. Appeal across product standards will be assessed in a controlled laboratory and using ecological momentary assessment. Ethics and dissemination The protocol was approved by the University of Oklahoma Health Sciences Center Institutional Review Board (#11865). Findings will examine the effects of a reduced nicotine standard and a menthol ban on young adult smoking and will be disseminated through peer-reviewed journal articles and presentations at scientific conferences. Trial registration number NCT04340947

    Visuospatial Processing Deficits Linked to Posterior Brain Regions in Premanifest and Early Stage Huntington's Disease.

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    OBJECTIVES: Visuospatial processing deficits have been reported in Huntington's disease (HD). To date, no study has examined associations between visuospatial cognition and posterior brain findings in HD. METHODS: We compared 119 premanifest (55> and 64<10.8 years to expected disease onset) and 104 early symptomatic (59 stage-1 and 45 stage-2) gene carriers, with 110 controls on visual search and mental rotation performance at baseline and 12 months. In the disease groups, we also examined associations between task performance and disease severity, functional capacity and structural brain measures. RESULTS: Cross-sectionally, there were strong differences between all disease groups and controls on visual search, and between diagnosed groups and controls on mental rotation accuracy. Only the premanifest participants close to onset took longer than controls to respond correctly to mental rotation. Visual search negatively correlated with disease burden and motor symptoms in diagnosed individuals, and positively correlated with functional capacity. Mental rotation ("same") was negatively correlated with motor symptoms in stage-2 individuals, and positively correlated with functional capacity. Visual search and mental rotation were associated with parieto-occipital (pre-/cuneus, calcarine, lingual) and temporal (posterior fusiform) volume and cortical thickness. Longitudinally, visual search deteriorated over 12 months in stage-2 individuals, with no evidence of declines in mental rotation. CONCLUSIONS: Our findings provide evidence linking early visuospatial deficits to functioning and posterior cortical dysfunction in HD. The findings are important since large research efforts have focused on fronto-striatal mediated cognitive changes, with little attention given to aspects of cognition outside of these areas. (JINS, 2016, 22, 595-608)

    Disrupted anatomic networks in the 22q11.2 deletion syndrome

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    AbstractThe 22q11.2 deletion syndrome (22q11DS) is an uncommon genetic disorder with an increased risk of psychosis. Although the neural substrates of psychosis and schizophrenia are not well understood, aberrations in cortical networks represent intriguing potential mechanisms. Investigations of anatomic networks within 22q11DS are sparse. We investigated group differences in anatomic network structure in 48 individuals with 22q11DS and 370 typically developing controls by analyzing covariance patterns in cortical thickness among 68 regions of interest using graph theoretical models. Subjects with 22q11DS had less robust geographic organization relative to the control group, particularly in the occipital and parietal lobes. Multiple global graph theoretical statistics were decreased in 22q11DS. These results are consistent with prior studies demonstrating decreased connectivity in 22q11DS using other neuroimaging methodologies

    Changes in Dietary Intake and Adherence to the NU-AGE Diet Following a One-Year Dietary Intervention among European Older Adults—Results of the NU-AGE Randomized Trial

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    Background: The Mediterranean Diet has been proposed as an effective strategy to reduce inflammaging, a chronic low grade inflammatory status, and thus, to slow down the aging process. We evaluated whether a Mediterranean-like dietary pattern specifically targeting dietary recommendations of people aged over 65 years (NU-AGE diet) could be effective to shift dietary intake of older adults towards a healthful diet. Methods: Adults aged 65–80 years across five EU-centers were randomly assigned to a NU-AGE diet group or control group. The diet group followed one year of NU-AGE dietary intervention specifying consumption of 15 food groups plus the use of a vitamin D supplement. Participants in the diet group received counselling and individually tailored dietary advice, food products and a vitamin D supplement. Dietary intake was assessed by means of seven-day food records at baseline and one-year follow-up. A continuous NU-AGE index (0–160 points) was developed to assess NU-AGE diet adherence. Results: In total 1296 participants were randomized and 1141 participants completed the intervention (571 intervention, 570 control). After one year, the diet group improved mean intake of 13 out of 16 NU-AGE dietary components (p < 0.05), with a significant increase in total NU-AGE index (difference in mean change = 21.3 ± 15.9 points, p < 0.01). Conclusions: The NU-AGE dietary intervention, based on dietary recommendations for older adults, consisting of individual dietary counselling, free healthy foods and a vitamin D supplement, may be a feasible strategy to improve dietary intake in an aging European population

    The ENIGMA Stroke Recovery Working Group: Big data neuroimaging to study brain–behavior relationships after stroke

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    The goal of the Enhancing Neuroimaging Genetics through Meta‐Analysis (ENIGMA) Stroke Recovery working group is to understand brain and behavior relationships using well‐powered meta‐ and mega‐analytic approaches. ENIGMA Stroke Recovery has data from over 2,100 stroke patients collected across 39 research studies and 10 countries around the world, comprising the largest multisite retrospective stroke data collaboration to date. This article outlines the efforts taken by the ENIGMA Stroke Recovery working group to develop neuroinformatics protocols and methods to manage multisite stroke brain magnetic resonance imaging, behavioral and demographics data. Specifically, the processes for scalable data intake and preprocessing, multisite data harmonization, and large‐scale stroke lesion analysis are described, and challenges unique to this type of big data collaboration in stroke research are discussed. Finally, future directions and limitations, as well as recommendations for improved data harmonization through prospective data collection and data management, are provided

    Online social networking and psychological experiences:the perceptions of young people with mental health difficulties

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    Objectives This study explores the interaction between online social networking experiences and wellbeing in 12 young people accessing mental health services. Methods Data from semi-structured interviews was analysed using Grounded Theory methodology. Results “Threats and judgement” and “connection and support” were experienced by adolescents, facilitated by having continuous access to a vast social network. These experiences influenced adolescents' psychological wellbeing, mediated by their responses to threat and judgement and maintaining “safe sharing” with their network. Social network use was conceived as a gamble of balancing its potentially positive and negative impact in a culture in which social network use appears to be unavoidable. Conclusions The findings indicate the importance of routine assessment and formulation of social networking use in understanding adolescents' psychological distress. Furthermore, a range of opportunities exist for clinicians to utilise the anonymity and peer support that social networks offer to broaden the range of mental health services offered to young people
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