The effect of atomic-scale defects and dopants on graphene electronic structure

Graphene, being one-atom thick, is extremely sensitive to the presence of adsorbed atoms and molecules and, more generally, to defects such as vacancies, holes and/or substitutional dopants. This property, apart from being directly usable in molecular sensor devices, can also be employed to tune graphene electronic properties. Here we briefly review the basic features of atomic-scale defects that can be useful for material design. After a brief introduction on isolated $p_z$ defects, we analyse the electronic structure of multiple defective graphene substrates, and show how to predict the presence of microscopically ordered magnetic structures. Subsequently, we analyse the more complicated situation where the electronic structure, as modified by the presence of some defects, affects chemical reactivity of the substrate towards adsorption (chemisorption) of atomic/molecular species, leading to preferential sticking on specific lattice positions. Then, we consider the reverse problem, that is how to use defects to engineer graphene electronic properties. In this context, we show that arranging defects to form honeycomb-shaped superlattices (what we may call "supergraphenes") a sizeable gap opens in the band structure and new Dirac cones are created right close to the gapped region. Similarly, we show that substitutional dopants such as group IIIA/VA elements may have gapped quasi-conical structures corresponding to massive Dirac carriers. All these possible structures might find important technological applications in the development of graphene-based logic transistors.Comment: 16 pages, 14 figures, "Physics and Applications of Graphene - Theory" - Chapter 3, http://www.intechweb.org/books/show/title/physics-and-applications-of-graphene-theor

Band engineering in graphene with superlattices of substitutional defects

We investigate graphene superlattices of nitrogen and boron substitutional defects and by using symmetry arguments and electronic structure calculations we show how such superlattices can be used to modify graphene band structure. Specifically, depending on the superlattice symmetry, the structures considered here can either preserve the Dirac cones (D_{6h} superlattices) or open a band gap (D_{3h}). Relevant band parameters (carriers effective masses, group velocities and gaps, when present) are found to depend on the superlattice constant n as 1/n^{p} where p is in the range 1-2, depending on the case considered. Overall, the results presented here show how one can tune the graphene band structure to a great extent by modifying few superlattice parameters.Comment: accepted, J. Phys. Chem.

Symmetry-induced gap opening in graphene superlattices

We study nxn honeycomb superlattices of defects in graphene. The considered defects are missing p_z orbitals and can be realized by either introducing C atom vacancies or chemically binding simple atomic species at the given sites. Using symmetry arguments we show how it is possible to open a gap when n=3m+1,3m+2 (m integer), and estimate its value to have an approximate square-root dependence on the defect concentration x=1/n^2. Tight-binding calculations confirm these findings and show that the induced-gaps can be quite large, e.g. ~100 meV for x~10^{-3}. Gradient-corrected density functional theory calculations on a number of superlattices made by H atoms adsorbed on graphene are in good agreement with tight-binding results, thereby suggesting that the proposed structures may be used in practice to open a gap in graphene.Comment: 5 pages, 4 figure

The Switched Mode Power Amplifiers

Non

Five shades of women: evidence from Italian listed firms

Purpose This paper aims to examine empirically the impact of gender diversity on corporate performance by both comparing different positions occupied by female directors on the boards and their personal-specific characteristics. Design/methodology/approach The paper examines a sample of Italian listed companies during 2006\u20132015. To deal with endogeneity issues, the authors use a generalized method of moments as an empirical methodology. Findings The empirical findings show that the positive effect of both independent and executive women directors on firm performance is moderated by the specific characteristics of female directors. Specifically, the analyses show that foreign and busy females negatively impact on performance. Conversely, graduate female directors strengthen the positive link between executive women and firm performance. Originality/value The paper sheds light on the consequences of appointing different types of female directors (i.e. independent, executive, graduate, foreign and busy) on firm performance. Our empirical research that investigates the association between gender diversity and performance in the Italian context based on a longitudinal study, which involves a period of ten\u2009years, allowing consideration both of the years before and after the introduction of the gender quota law (Golfo\u2013Mosca law)

The Doherty Power Amplifier

Non

Understanding adsorption of hydrogen atoms on graphene

Adsorption of hydrogen atoms on a single graphite sheet (graphene) has been investigated by first-principles electronic structure means, employing plane-wave based, periodic density functional theory. A reasonably large 5x5 surface unit cell has been employed to study single and multiple adsorption of H atoms. Binding and barrier energies for sequential sticking have been computed for a number of configurations involving adsorption on top of carbon atoms. We find that binding energies per atom range from ~0.8 eV to ~1.9 eV, with barriers to sticking in the range 0.0-0.2 eV. In addition, depending on the number and location of adsorbed hydrogen atoms, we find that magnetic structures may form in which spin density localizes on a $\sqrt{3}{x}\sqrt{3}{R}30^{\circ}$ sublattice, and that binding (barrier) energies for sequential adsorption increase (decrease) linearly with the site-integrated magnetization. These results can be rationalized with the help of the valence-bond resonance theory of planar $\pi$ conjugated systems, and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.Comment: 12 pages, 8 figures and 4 table

Role of Body Weight in the Onset and the Progression of Idiopathic Premature Pubarche

Background: The term premature pubarche (PP) refers to the appearance of pubic hair before age 8 in girls and before age 9 in boys. Although idiopathic PP (often associated with premature adrenarche) is considered an extreme variation from the norm, it may be an initial sign of persistent hyperandrogenism. Factors contributing to PP onset and progression have not been identified to date. Aims: The objectives of this study are to describe a group of Italian children with PP, to identify potential factors for its onset, and to define its clinical and biochemical progression. Methods: We retrospectively enrolled all infants born between 2001 and 2014 with PP. Children with advanced bone age (BA) underwent functional tests to determine the cause of PP. Hormonal analysis and BA determination were performed annually during a 4-year follow-up period. Results: A total of 334 children with PP were identified: idiopathic PP (92.5%, associated with premature adrenarche in some cases); related to precocious puberty (6.6%); late-onset 21-hydroxylase deficiency (0.9%). Low birth weight was associated with premature adrenal activation. Body mass index (BMI) was the only factor that influenced the progression of BA during follow-up. Conclusions: Low birth weight is a predisposing factor for premature adrenal activation. The increase in BMI in patients with idiopathic PP during the 4-years of follow-up was responsible for BA acceleration. We recommend prevention of excessive weight gain in children with PP and strict adherence to follow-up in order to prevent serious metabolic consequences

Corrigendum to a new neurocognitive interpretation of shoulder position sense during reaching:unexpected competence in the measurement of extracorporeal space

[This corrects the article DOI: 10.1155/2016/9065495.

Coverage and invariance for the biological control of pests in mediterranean greenhouses

A major problem related to the treatment of ecosystems is that they have no available mathematical formalization. This implies that many of their properties are not presented as short, rigorous modalities, but rather as long expressions which, from a biological standpoint, totally capture the significance of the property, but which have the disadvantage of not being sufficiently manageable, from a mathematical standpoint. The interpretation of ecosystems through networks allows us to employ the concepts of coverage and invariance alongside other related concepts. The latter will allow us to present the two most important relations in an ecosystem – predator–prey and competition – in a different way. Biological control, defined as “the use of living organisms, their resources or their products to prevent or reduce loss or damage caused by pests”, is now considered the environmentally safest and most economically advantageous method of pest control (van Lenteren, 2011). A guild includes all those organisms that share a common food resource (Polis et al., 1989), which in the context of biological control means all the natural enemies of a given pest. There are several types of intraguild interactions, but the one that has received most research attention is intraguild predation, which occurs when two organisms share the same prey while at the same time participating in some kind of trophic interaction. However, this is not the only intraguild relationship possible, and studies are now being conducted on others, such as oviposition deterrence. In this article, we apply the developed concepts of structural functions, coverage, invariant sets, etc. (Lloret et al., 1998, Esteve and Lloret, 2006a, Esteve and Lloret, 2006b and Esteve and Lloret, 2007) to a tritrophic system that includes aphids, one of the most damaging pests and a current bottleneck for the success of biological control in Mediterranean greenhouses