131,622 research outputs found
Optical properties of one-dimensional graphene polymers: the case of polyphenanthrene
No full textWe investigate from first principles the effect of many-body corrections on the optoelectronic properties of polyphenanthrene (PPh), a prototype system for carbon-based ladder polymers and I D nanographenes with cis-polyene edges. We show that the inclusion of many-body effects is essential to correctly describe both quasiparticle bandstructure and optical response. Consistently with the reduced dimensionality of the system, the inclusion of electron-hole interaction leads to strongly bound excitons which dominate the spectra. A complete characterization of the low-energy excitonic states is carried out, together with their optical activity. In particular, we find a dark exciton below the first optically active one, which is expected to crucially affect the luminescence efficiency. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.We investigate from first principles the effect of many-body corrections on the optoelectronic properties of polyphenanthrene (PPh), a prototype system for carbon-based ladder polymers and 1D nanographenes with cis-polyene edges. We show that the inclusion of many-body effects is essential to correctly describe both quasiparticle bandstructure and optical response. Consistently with the reduced dimensionality of the system, the inclusion of electron-hole interaction leads to strongly bound excitons which dominate the spectra. A complete characterization of the low-energy excitonic states is carried out, together with their optical activity. In particular, we find a dark exciton below the first optically active one, which is expected to crucially affect the luminescence efficiency. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA,
Subjective and psychological well-being in Parkinson's Disease: A systematic review
No full textObjectives: The aim of this review is to summarize studies investigating subjective and psychological well-being in patients with Parkinson's disease (PD). Materials and Methods: A systematic and integrative review according to PRISMA criteria was performed with a literature search from inception up to September 2017 in multidisciplinary databases (PubMED, Scopus, Web of Knowledge) by combining together key words related to PD and well-being. Studies were included if: their full-text was available; they involved PD patients; focused on the selected positive dimensions; written in English. Case studies, conference proceedings, abstract, dissertations, book chapters, validation studies and reviews were excluded. Data extracted from the studies included sample characteristics, the positive dimension investigated, type of measure, study aims, design and results. One reviewer extracted details and commented results with other reviewers. The studies’ quality was assessed following Kmet, Lee, and Cook. Results: Out of 1425 studies extracted, 12 studies (9 quantitative, 2 qualitative, 1 mixed methods) involving 2204 patients with PD were included. Most of the studies had a cross-sectional design and/or evaluated the effect of physical rehabilitation on well-being. Articles documented that the illness could impair well-being for its progressive impact on patients’ motor autonomy. Preserving motor and musculoskeletal functioning facilitate patients’ experience of well-being, social contribution and the maintenance of their job. Conclusions: Research on positive resources in PD is still scarce compared to other chronic illnesses. The few available investigations suggest the need of preserving motor abilities by proper rehabilitation programs for maintaining and/or promoting patients’ well-being and life engagement
Quantum dot states and optical excitations of edge-modulated graphene nanoribbons
No full textWe investigate from first principles the electronic and optical properties of edge-modulated armchair graphene nanoribbons, including both quasiparticle corrections and excitonic effects. Exploiting the oscillating behavior of the ribbon energy gap, we show that minimal width-modulations are sufficient to obtain confinement of both electrons and holes, thus forming optically active quantum dots with unique properties, such as the coexistence of dotlike and extended excitations and the fine tunability of optical spectra, with great potential for optoelectronic applications
Les premiers symboles musicaux chrétiens
No full texttraduction français de l'article paru dans l' Atlante storico della musica nel Medioev
Tree-designs with balanced-type conditions
No full textFor a given graph G we say that a G-design is balanced if there exists a constant r such that for each point x the number of blocks containing x is equal to r. A G-design is degree-balanced if, for each degree d occurring in the graph G, there exists a constant r_d such that, for each point x, the number of blocks containing x as a vertex of degree d is equal to r_d.Let V_1, V_2, . . . , V_h be the vertex-orbits of G under its automorphism group. A G-design is said to be orbit-balanced (or strongly balanced) if for i = 1, 2, . . . , h there exists a constant R_i such that, for each point x the number of blocks of the G-design in which x occurs as an element in the orbit V_i is equal to R_i.If G is a tree with six vertices, we determine the values of v for which a balanced G-design with v points exists, the values of v for which a degree-balanced G-design with v points exists, and the values of v for which an orbit-balanced G-design with v points exists.We also consider the existence problem for G-designs which are not balanced, which are balanced but not degree-balanced, and which are degree-balanced but not orbit-balanced
Publisher's Note: Optical properties of graphene nanoribbons: The role of many-body effects (Physical Review B - Condensed Matter and Materials Physics (2008) 77, (041404))
No full textGrafi cubici e gruppi di automorfismo
No full textIn questa presentazione esporremmo alcuni risultati riguardanti automorfismi di grafi cubici, come ad esempio: a) alcune condizioni per le quali un automorfismo di un grafo agisce su particolari sottografi come l'automorfismo banale o un automorfismo non banale; b) l'esistenza di cinque famiglie infinite che soddisfano le condizioni di cui sopra; c) la determinazione dei gruppi di automorfismo di sette famiglie infinite di grafi cubici connessi con girth 5, cinque delle quali costituite da grafi detti snarks; d) per ogni intero positivo m, l'esistenza di grafi cubici (snarks) con 24+4m o 26+4m vertici aventi gruppi di automorfismi banali, di un grafo cubico con 24+4m vertici avente gruppo di automorfismo isomorfo al gruppo ciclico di ordine 2, di un grafo cubico con 18+16m vertici avente gruppo di automorfismo di ordine 2^{m+2}; e) per ogni intero positivo dispari k, k>3, l'esistenza di un grafo cubico (snarks) di ordine 4k ed un grafo cubico (snark) di ordine 8k con gruppo di automorfismo isomorfo al gruppo diedrale di ordine 4k
Numerically Precise Benchmark of Many-Body Self-Energies on Spherical Atoms
No full text[Image: see text] We investigate the performance of beyond-GW approaches in many-body perturbation theory by addressing atoms described within the spherical approximation via a dedicated numerical treatment based on B-splines and spherical harmonics. We consider the GW, second Born (2B), and GW + second order screened exchange (GW+SOSEX) self-energies and use them to obtain ionization potentials from the quasi-particle equation (QPE) solved perturbatively on top of independent-particle calculations. We also solve the linearized Sham–Schlüter equation (LSSE) and compare the resulting xc potentials against exact data. We find that the LSSE provides consistent starting points for the QPE but does not present any practical advantage in the present context. Still, the features of the xc potentials obtained with it shed light on possible strategies for the inclusion of beyond-GW diagrams in the many-body self-energy. Our findings show that solving the QPE with the GW+SOSEX self-energy on top of a PBE or PBE0 solution is a viable scheme to go beyond GW in finite systems, even in the atomic limit. However, GW shows a comparable performance if one agrees to use a hybrid starting point. We also obtain promising results with the 2B self-energy on top of Hartree–Fock, suggesting that the full time-dependent Hartree–Fock vertex may be another viable beyond-GW scheme for finite systems
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Adapted Physical Activity Can Increase Life Appreciation in Patients with Parkinson's Disease
No full textObjectives: This study aimed to measure the effect of a treatment of adapted physical activity (APA) on motor symptoms and on positive psychological resources in a group of patients with PD. Methods: 37 patients with PD (M age = 71.5; 70.3% male) completed measures of disability level, motor performance, distress, well-being, and quality of life before and after participating in a program of APA (duration: 7 months). Analysis of variance - repeated measures was performed to evaluate the effect of APA on disability, distress, and well-being. Results: After intervention, patients reported significant improvements in their motor autonomy, disability level, psychological distress, and in life appreciation. Discussion: A brief physical activity program was beneficial not only to patients’ motor functioning, but also to their mental health, by reducing distress and promoting life appreciation
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