579 research outputs found
Parametric resonance of a two-dimensional electron gas under bichromatic irradiation
In an ultrahigh mobility 2D electron gas, even a weak nonparabolicity of the
electron dispersion, by violating Kohn's theorem, can have a drastic effect on
dc magnetotransport under ac drive. We study theoretically the manifestation of
this effect in the dc response to the combined action of two driving ac-fields
(bichromatic irradiation). Compared to the case of monochromatic irradiation,
which is currently intensively studied both experimentally and theoretically,
the presence of a second microwave source provides additional insight into the
properties of an ac-driven 2D electron gas. In particular, we find that
nonparabolicity, being the simplest cause for a violation of Kohn's theorem,
gives rise to new qualitative effects specific to bichromatic irradiation.
Namely, when the frequencies and are well away from the
cyclotron frequency, , our simple classical considerations
demonstrate that the system becomes parametrically unstable with respect to
fluctuations with frequency . As an additional effect of
nonparabolicity, this parametric instability can manifest itself in the dc
properties of the system. This happens when , and
are related as 3:1:2, respectively. Even for weak detuning between
and , the effect of the bichromatic irradiation on the dc
response in the presence of nonparabolicity can differ dramatically from the
monochromatic case. In particular, the equations of motion can acquire
multistable solutions. As a result, the diagonal dc-conductivity can assume
several stable negative values at the same magnetic field.Comment: 11 pages, 10 figure
Geometric characterization of nodal domains: the area-to-perimeter ratio
In an attempt to characterize the distribution of forms and shapes of nodal
domains in wave functions, we define a geometric parameter - the ratio
between the area of a domain and its perimeter, measured in units of the
wavelength . We show that the distribution function can
distinguish between domains in which the classical dynamics is regular or
chaotic. For separable surfaces, we compute the limiting distribution, and show
that it is supported by an interval, which is independent of the properties of
the surface. In systems which are chaotic, or in random-waves, the
area-to-perimeter distribution has substantially different features which we
study numerically. We compare the features of the distribution for chaotic wave
functions with the predictions of the percolation model to find agreement, but
only for nodal domains which are big with respect to the wavelength scale. This
work is also closely related to, and provides a new point of view on
isoperimetric inequalities.Comment: 22 pages, 11 figure
Reproductive period and preclinical cerebrospinal fluid markers for Alzheimer disease: a 25-year study
OBJECTIVE: The aim of the study was to examine the association between reproductive period, as an indicator of endogenous estrogen, and levels of cerebrospinal fluid (CSF) biomarkers for Alzheimer disease (AD). METHODS: A population-based sample of women from Gothenburg, Sweden was followed from 1968 to 1994 (Nâ=â75). All women had natural menopause and were free from dementia. Information on reproductive period (age at menarche to age at menopause) was obtained from interviews from 1968 to 1980. Lumbar puncture was performed from 1992 to 1994 and CSF levels of AÎČ42, AÎČ40, P-tau, and T-tau were measured with immunochemical methods. Linear regression models adjusted for potential confounders were used to analyze the relationship between reproductive period and CSF biomarkers for AD. RESULTS: Longer reproductive period was associated with lower levels of AÎČ42 (ÎČâ=â-19.2, Pâ =â0.01), higher levels of P-tau (ÎČâ=â0.03, Pâ =â0.01), and lower ratio of AÎČ42/AÎČ40 (ÎČâ=â-0.02, Pâ =â0.01), while no association was observed for T-tau (ÎČâ=â0.01, Pâ =â0.46). In separate analyses, examining the different components of reproductive period, earlier age at menarche was associated higher levels of P-tau (ÎČâ=â-0.07, Pâ =â0.031) and lower ratio of AÎČ42/AÎČ40 (ÎČâ=â0.05, Pâ =â0.021), whereas no association was observed with AÎČ42 (ÎČâ=â31.1, Pâ =â0.11) and T-tau (ÎČâ=â-0.001, Pâ =â0.98). Furthermore, no association was observed between age at menopause and CSF biomarkers for AD. CONCLUSIONS: Our findings suggest that longer exposure to endogenous estrogen may be associated with increased levels of AD biomarkers in the preclinical phase of AD. These findings, however, need to be confirmed in larger samples. / Video Summary: http://links.lww.com/MENO/A804
Polygenic risk scores for Alzheimer's disease are related to dementia risk in APOE É4 negatives
Introduction: Studies examining the effect of polygenic risk scores (PRS) for Alzheimer's disease (AD) and apolipoprotein E (APOE) genotype on incident dementia in very old individuals are lacking. /
Methods: A populationâbased sample of 2052 individuals ages 70 to 111, from Sweden, was followed in relation to dementia. ADâPRSs including 39, 57, 1333, and 13,942 single nucleotide polymorphisms (SNPs) were used. /
Results: ADâPRSs (including 39 or 57 SNPs) were associated with dementia (57âSNPs ADâPRS: hazard ratio 1.09, confidence interval 1.01â1.19, P = .03), particularly in APOE É4 nonâcarriers (57âSNPs ADâPRS: 1.15, 1.05â1.27, P = 4 Ă 10â3, 39âSNPs ADâPRS: 1.22, 1.10â1.35, P = 2 Ă 10â4). No association was found with the other ADâPRSs. Further, APOE É4 was associated with increased risk of dementia (1.60, 1.35â1.92, P = 1 Ă 10â7). In those aged â„95 years, the results were similar for the ADâPRSs, while APOE É4 only predicted dementia in the lowârisk tertile of ADâPRSs. /
Discussion: These results provide information to identify individuals at increased risk of dementia
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Dominant cognitive frames and the innovative power of social networks
In this paper, we illustrate the link between social network structures, dominant cognitive frames on network purpose and the innovative power of a network, through a mixed-method comparative analysis of two Knowledge Translation Networks (KTNs)in the English National Health Service (NHS). Our findings illustrate several challenges for networked forms of organization linked to different manifestations of social networks (centralized/decentralized) and dominant cognitive frames (polarizing/loosely clustered). Our paper contributes a better understanding of how dominant frames on network purpose emerge alongside the development of network structure itself, and explores how this interplay between dominant frames and social networks impacts upon the collaborative work that supports the networksâ innovative power
Heidegger on creativity: From boredom to re-engagement with the world
Experimental psychologists have discussed whether boredom can help us become more creative. At ïŹrst blush, this would seem to be rather unlikely. When we are bored, we are disengaged; we cannot be bothered and nothing seems worthwhile; we have no interest in the world around us. Such a condition, surely, is not conducive to creativity (Haager et al. 2018). Yet some psychologists disagree (Gasper and Middlewood 2014). Boredom, they explain, breaks down entrenched routines and thought-patterns and provides us with an opportunity to think again and anew. Respondents in âapproach-oriented statesâ such as boredom engage in more âassociative thoughtâ than those in âavoidance-oriented affective states.â This is how boredom comes to encourage âthe quest for meaning and explorationâ (Gasper and Middlewood 2014, pp. 53â55...2-s2.0-8508440789
Reculturing schools in England: how âcultâ values in education policy discourse influence the construction of practitioner identities and work orientations
The imperative of continuous improvement has now become normative in education policy discourse, typically framed as setting âaspirationalâ targets for pupil performance as a prerequisite for gaining competitive advantage in the global economy. In this context, teachers, leaders, teacher assistants and other practitioners working in schools across England have been under increasing pressure to raise standards. This article focuses on how values are deployed in reculturing and regulating practitioners to develop identities and work orientations which are congruent with the policymakersâ agendas. G.H. Meadâs concept of âcultâ values illuminates the process of fostering homogeneity with the dominant policy discourse through an inclusion/exclusion dynamic. Interview data collected in two primary schools revealed a significant convergence of practitioner discourse with policy objectives. Delivering improvement affects how practitioners talk about their work and see themselves as educators. The âcultâ of continuous improvement appears to inhibit a critical approach to the implementation of education policies by school practitioners in their everyday work
Decentring emotion regulation: from emotion regulation to relational emotion
YesThis article takes a critical approach to emotion regulation suggesting that the concept needs supplementing with a relational position on the generation and restraint of emotion. I chart the relational approach to emotion, challenging the âtwo-stepâ model of emotion regulation. From this, a more interdisciplinary approach to emotion is developed using concepts from social science to show the limits of instrumental, individualistic and cognitivist orientations in the psychology of emotion regulation, centred on appraisal theory. Using a social interactionist approach I develop an ontological position in which social relations form the fundamental contexts in which emotions are generated, toned, and restrained, so that regulation is decentred and seen as just one moment or aspect in the relational patterning of emotion
PERFIL DE VIOLĂNCIA NA INFĂNCIA E ADOLESCĂNCIA EM IPAMERI - GOIĂS
O artigo pretende traçar um perfil da violĂȘncia contra a criança e adolescente notificados na cidade de Ipameri, estado de GoiĂĄs. Trata-se de investigação descritiva, retrospectiva e quantitativa realizada por meio de anĂĄlise documental, a partir das fichas de atendimento das ocorrĂȘncias de violĂȘncia registradas no Conselho Tutelar, nos anos de 2012 e 2013. Os dados sĂŁo apresentados por meio de estatĂstica descritiva. Totalizaram-se 546 registros de violĂȘncia, sendo 338 casos de negligĂȘncia, 103 casos de violĂȘncia sexual, 72 casos de violĂȘncia fĂsica e 34 casos de violĂȘncia psicolĂłgica. O sexo feminino Ă© o mais acometido. Em todos os tipos de violĂȘncia o principal agressor Ă© intrafamiliar e a faixa etĂĄria mais acometida Ă© a de cinco a nove anos de idade. A atuação dos profissionais de saĂșde Ă© fundamental no processo de identificação dos maus tratos, do agressor, favorecendo momentos participativos de educação e promoção da saĂșde com familiares e a rede de proteção intersetorial local
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