989 research outputs found

    Are epistemological beliefs and motivational strategies related to study engagement in higher education?

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    3rd International Conference on Education and Educational Psychology (ICEEPSY), Istanbul, TURKEY, OCT 10-13, 2012Peer reviewe

    Electronic shell and supershell structure in graphene flakes

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    We use a simple tight-binding (TB) model to study electronic properties of free graphene flakes. Valence electrons of triangular graphene flakes show a shell and supershell structure which follows an analytical expression derived from the solution of the wave equation for triangular cavity. However, the solution has different selection rules for triangles with armchair and zigzag edges, and roughly 40000 atoms are needed to see clearly the first supershell oscillation. In the case of spherical flakes, the edge states of the zigzag regions dominate the shell structure which is thus sensitive to the flake diameter and center. A potential well that is made with external gates cannot have true bound states in graphene due to the zero energy band gap. However, it can cause strong resonances in the conduction band.Comment: Presented in the ISSPIC-14 conference, Valladolid, September 200

    Electronic structure of triangular, hexagonal and round graphene flakes near the Fermi level

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    The electronic shell structure of triangular, hexagonal and round graphene quantum dots (flakes) near the Fermi level has been studied using a tight-binding method. The results show that close to the Fermi level the shell structure of a triangular flake is that of free massless particles, and that triangles with an armchair edge show an additional sequence of levels ("ghost states"). These levels result from the graphene band structure and the plane wave solution of the wave equation, and they are absent for triangles with an zigzag edge. All zigzag triangles exhibit a prominent edge state at the Fermi level, and few low-energy conduction electron states occur both in triangular and hexagonal flakes due to symmetry reasons. Armchair triangles can be used as building blocks for other types of flakes that support the ghost states. Edge roughness has only a small effect on the level structure of the triangular flakes, but the effect is considerably enhanced in the other types of flakes. In round flakes, the states near the Fermi level depend strongly on the flake radius, and they are always localized on the zigzag parts of the edge

    Edge-dependent selection rules in magic triangular graphene flakes

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    The electronic shell and supershell structure of triangular graphene quantum dots has been studied using density functional and tight-binding methods. The density functional calculations demonstrate that the electronic structure close to the Fermi energy is correctly described with a simple tight-binding model where only the p_z orbitals perpendicular to the graphene layer are included. The results show that (i) both at the bottom and at the top of the p_z band a supershell structure similar to that of free electrons confined in a triangular cavity is seen, (ii) close to the Fermi level the shell structure is that of free massless particles, (iii) triangles with armchair edges show an additional sequence of levels ('ghost states') absent for triangles with zigzag edges while the latter exhibit edge states, and (iv) the observed shell structure is rather insensitive to the edge roughness

    Exploring methods for predicting multiple pressures on ecosystem recovery: A case study on marine eutrophication and fisheries

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    AbstractEfforts to attain good environmental status in the marine realm require decisions which cannot be done without knowledge of effects of different management measures. Given the wide diversity of marine ecosystems, multitude of pressures affecting it and the still poor understanding on linkages between those, there are likely no models available to give all the required answers. Hence, several separate approaches can be used in parallel to give support for management measures. We tested three completely different methods – a spatial impact index, a food web model and a Bayesian expert method. We found that a large uncertainty existed regarding the ecosystem response to the management scenarios, and that the three different modelling approaches complemented each other. The models indicated that in order to reach an improved overall state of the ecosystem nutrient reductions are the more effective of the two management variables explored, and that cumulative effects of the management of nutrient inputs and fishing mortality are likely to exist

    Trends in gambling participation and gambling severity among Finnish men and women: cross-sectional population surveys in 2007, 2010 and 2015

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    Objective The aim of this study is to evaluate trends in past-year gambling participation and gambling severity among Finnish men and women from 2007 to 2015.Design Cross-sectional population surveys from years 2007, 2011 and 2015.Setting Data were drawn from the population register and collected using computer-assisted telephone interviews.Participants Representative random samples of Finns aged 15-74 were drawn in the study in 2007 (n=5008), 2011 (n=4484) and 2015 (n=4515) with response rates of 58%, 40% and 62%, respectively.Outcome measures The outcome measures were gambling versatility, type of games, gambling intensity and gambling severity. Significance (p) between time points was determined using (2) tests. All temporal comparisons between 2007-2011, 2011-2015 and 2007-2015 were performed separately for all respondents aged 15-74 and for women and men.Results Gambling participation overall showed a rising trend (6.6 percentage points, 95%CI 4.9 to 8.3) from 2007 to 2015. In 2007-2011 women's gambling participation increased more (7.8 percentage points, 95%CI 5.5 to 10.4) than men's (5.4 percentage points, 95%CI 3.2 to 7.6). The most popular game types since 2007 have been lottery games, scratch cards and electronic gaming machines (EGMs). EGM gambling, on the other hand, has decreased since 2007. Online gambling has increased significantly from 2007 to 2015 in both genders. Men's at-risk gambling decreased from 2007 to 2011, while women's at-risk gambling and problem gambling increased from 2011 to 2015.Conclusions Women's increasing gambling participation is causing gender differences in gambling behaviour to narrow. The article concludes with a discussion of the need for gender-specific interventions aimed at preventing gambling-related harm and ultimately at protecting the most vulnerable groups

    Sleep-wake sensitive mechanisms of adenosine release in the basal forebrain of rodents : an in vitro study

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    Adenosine acting in the basal forebrain is a key mediator of sleep homeostasis. Extracellular adenosine concentrations increase during wakefulness, especially during prolonged wakefulness and lead to increased sleep pressure and subsequent rebound sleep. The release of endogenous adenosine during the sleep-wake cycle has mainly been studied in vivo with microdialysis techniques. The biochemical changes that accompany sleep-wake status may be preserved in vitro. We have therefore used adenosine-sensitive biosensors in slices of the basal forebrain (BFB) to study both depolarization-evoked adenosine release and the steady state adenosine tone in rats, mice and hamsters. Adenosine release was evoked by high K+, AMPA, NMDA and mGlu receptor agonists, but not by other transmitters associated with wakefulness such as orexin, histamine or neurotensin. Evoked and basal adenosine release in the BFB in vitro exhibited three key features: the magnitude of each varied systematically with the diurnal time at which the animal was sacrificed; sleep deprivation prior to sacrifice greatly increased both evoked adenosine release and the basal tone; and the enhancement of evoked adenosine release and basal tone resulting from sleep deprivation was reversed by the inducible nitric oxide synthase (iNOS) inhibitor, 1400 W. These data indicate that characteristics of adenosine release recorded in the BFB in vitro reflect those that have been linked in vivo to the homeostatic control of sleep. Our results provide methodologically independent support for a key role for induction of iNOS as a trigger for enhanced adenosine release following sleep deprivation and suggest that this induction may constitute a biochemical memory of this state
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