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 $\omega_1$ and $\omega_2$ are well away from the cyclotron frequency, $\omega_c$, our simple classical considerations demonstrate that the system becomes parametrically unstable with respect to fluctuations with frequency $(\omega_1+\omega_2)/2$. As an additional effect of nonparabolicity, this parametric instability can manifest itself in the dc properties of the system. This happens when $\omega_1$, $\omega_2$ and $\omega_c$ are related as 3:1:2, respectively. Even for weak detuning between $\omega_1$ and $\omega_2$, 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 $\rho$ between the area of a domain and its perimeter, measured in units of the wavelength $1/\sqrt{E}$. We show that the distribution function $P(\rho)$ 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 (N = 75). 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 Aβ42, Aβ40, 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 Aβ42 (β = -19.2, P  = 0.01), higher levels of P-tau (β = 0.03, P  = 0.01), and lower ratio of Aβ42/Aβ40 (β = -0.02, P  = 0.01), while no association was observed for T-tau (β = 0.01, P  = 0.46). In separate analyses, examining the different components of reproductive period, earlier age at menarche was associated higher levels of P-tau (β = -0.07, P  = 0.031) and lower ratio of Aβ42/Aβ40 (β = 0.05, P  = 0.021), whereas no association was observed with Aβ42 (β = 31.1, P  = 0.11) and T-tau (β = -0.001, P  = 0.98). 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 ɛ4 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 population‐based sample of 2052 individuals ages 70 to 111, from Sweden, was followed in relation to dementia. AD‐PRSs including 39, 57, 1333, and 13,942 single nucleotide polymorphisms (SNPs) were used. / Results: AD‐PRSs (including 39 or 57 SNPs) were associated with dementia (57‐SNPs AD‐PRS: hazard ratio 1.09, confidence interval 1.01–1.19, P = .03), particularly in APOE ɛ4 non‐carriers (57‐SNPs AD‐PRS: 1.15, 1.05–1.27, P = 4 × 10–3, 39‐SNPs AD‐PRS: 1.22, 1.10–1.35, P = 2 × 10–4). No association was found with the other AD‐PRSs. Further, APOE ɛ4 was associated with increased risk of dementia (1.60, 1.35–1.92, P = 1 × 10–7). In those aged ≥95 years, the results were similar for the AD‐PRSs, while APOE ɛ4 only predicted dementia in the low‐risk tertile of AD‐PRSs. / Discussion: These results provide information to identify individuals at increased risk of dementia

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 networks’ 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 first 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 “approach-oriented states” such as boredom engage in more “associative thought” than those in “avoidance-oriented affective states.” This is how boredom comes to encourage “the quest for meaning and exploration” (Gasper and Middlewood 2014, pp. 53–55...2-s2.0-8508440789

Reculturing schools in England: how ‘cult’ 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 ‘aspirational’ 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 policymakers’ agendas. G.H. Mead’s concept of ‘cult’ 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 ‘cult’ 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 ‘two-step’ 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 VIOLÊNCIA NA INFÂNCIA E ADOLESCÊNCIA EM IPAMERI - GOIÁS

O artigo pretende traçar um perfil da violência contra a criança e adolescente notificados na cidade de Ipameri, estado de Goiás. Trata-se de investigação descritiva, retrospectiva e quantitativa realizada por meio de análise documental, a partir das fichas de atendimento das ocorrências de violência registradas no Conselho Tutelar, nos anos de 2012 e 2013. Os dados são apresentados por meio de estatística descritiva. Totalizaram-se 546 registros de violência, sendo 338 casos de negligência, 103 casos de violência sexual, 72 casos de violência física e 34 casos de violência psicológica. O sexo feminino é o mais acometido. Em todos os tipos de violência o principal agressor é intrafamiliar e a faixa etária mais acometida é a de cinco a nove anos de idade. A atuação dos profissionais de saúde é fundamental no processo de identificação dos maus tratos, do agressor, favorecendo momentos participativos de educação e promoção da saúde com familiares e a rede de proteção intersetorial local