Theoretical study of structural and electronic properties of 2H-phase transition metal dichalcogenides

Computational physics and chemistry are called to play a very important role in the development of new technologies based on two-dimensional (2D) materials, reducing drastically the number of trial and error experiments needed to obtain meaningful advances in the field. Here, we present a thorough theoretical study of the structural and electronic properties of the single-layer, double-layer, and bulk transition metal dichalcogenides MoS2, MoSe2, MoTe2, WS2, WSe2, and WTe2 in the 2H phase, for which only partial experimental information is available. We show that the properties of these systems depend strongly on the density functional theory approach used in the calculations and that inclusion of weak dispersion forces is mandatory for a correct reproduction of the existing experimental data. By using the most accurate functionals, we predict interlayer separations, direct and indirect band gaps, and spin-orbit splittings in those systems for which there is no experimental information available. We also discuss the variation of these properties with the specific chalcogen and transition metal ato

Tunable plasmons in regular planar arrays of graphene nanoribbons with armchair and zigzag-shaped edges

Recent experimental evidence for and the theoretical confirmation of tunable edge plasmons and surface plasmons in graphene nanoribbons have opened up new opportunities to scrutinize the main geometric and conformation factors, which can be used to modulate these collective modes in the infrared-to-terahertz frequency band. Here, we show how the extrinsic plasmon structure of regular planar arrays of graphene nanoribbons, with perfectly symmetric edges, is influenced by the width, chirality and unit-cell length of each ribbon, as well as the in-plane vacuum distance between two contiguous ribbons. Our predictions, based on time-dependent density functional theory, in the random phase approximation, are expected to be of immediate help for measurements of plasmonic features in nanoscale architectures of nanoribbon devicesC.V.G. acknowledges the financial support of the “Secretaria Nacional de Educación Superior, Ciencia, Tecnología e Innovación” (SENESCYT-ECUADOR

Evaluation of an Interdisciplinary, Independent Study Module for History and Social Change: Fashion in the Sixties

Clothing, Textiles and Merchandisin

Acoustic plasmons in extrinsic free-standing graphene

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.An acoustic plasmon is predicted to occur, in addition to the conventional two-dimensional (2D) plasmon, as the collective motion of a system of two types of electronic carriers coexisting in the same 2D band of extrinsic (doped or gated) graphene. The origin of this novel mode stems from the anisotropy present in the graphene band structure near the Dirac points K and K'. This anisotropy allows for the coexistence of carriers moving with two distinct Fermi velocities along the γK and γK' directions, which leads to two modes of collective oscillation: one mode in which the two types of carriers oscillate in phase with one another (this is the conventional 2D graphene plasmon, which at long wavelengths (q → 0) has the same dispersion, q1/2, as the conventional 2D plasmon of a 2D free electron gas), and the other mode found here corresponds to a low-frequency acoustic oscillation (whose energy exhibits at long-wavelengths a linear dependence on the 2D wavenumber q) in which the two types of carriers oscillate out of phase. This prediction represents a realization of acoustic plasmons originated in the collective motion of a system of two types of carriers coexisting within the same band. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.MP acknowledges the financial support of MIUR (FIRB-Futuro in Ricerca 2010—Project PLASMOGRAPH grant no. RBFR10M5BT), the European Commission, the European Social Fund and Regione Calabria, (POR) Calabria—FSE 2007/2013. VMS acknowledges financial support from the Spanish MICINN (no. FIS2010-19609-C02-01), the Departamento de Educación del Gobierno Vasco, and the University of the Basque Country (no. GIC07-IT-366-07).Peer Reviewe

Breves considerações sobre a lei aplicável ao contrato de seguro

Resumo: Em 1 de Janeiro de 2009, entrou em vigor em Portugal o Decreto-Lei n.º 72/2008, de 16 de Abril, que aprovou um novo regime jurídico para o contrato de seguro. Este diploma contém, nos seus artigos 5.º a 10.º, regras destinadas a determinar a lei competente para regular o contrato de seguro internacional. Tais regras vieram substituir as que anteriormente transpuseram, para a ordem jurídica nacional, as Directivas comunitárias sobre a matéria. No entanto, a sua aplicação ficou muito prejudicada pela entrada em vigor do Regulamento Roma I. Neste estudo faz-se uma breve análise dos artigos 5.º a 10.º do novo regime jurídico do contrato de seguro, bem como dos preceitos internos por eles revogados e das regras sobre direito aplicável constantes das Directivas 88/357/CEE e 2002/83/CE. Numa última parte, serão estudadas as importantes normas de conflitos do Regulamento Roma I. Palavras-chave: Decreto-Lei n.º 72/2008, Convenção de Roma, Regulamento Roma I, Directiva 88/357/CEE, Directiva 2002/83/CE, Decreto-Lei n.º 94-B/98, contrato de seguro, contrato de seguro internacional, lei aplicável, Direito aplicável, regras de conflitos, Direito de conflitos, risco, compromisso, normas de aplicação imediata. Abstract: On the 1st of January 2009, a new legal regime regarding insurance contracts entered into force in Portugal. Approved by Decree-Law no. 72/2008, such regime contains, in its articles 5 to 10, new conflicts of law rules on international insurance contracts, which have replaced the former domestic conflicts rules approved by Decree-Law no. 94-B/98. Both Decree-Law no. 94-B/98 and Decree-Law no. 72/2008 aimed to transpose into Portuguese legal system the EU Directives on insurance contracts. Notwithstanding, the scope of application of articles 5 to 10 became severely affected when Rome I Regulation entered into force on December 17, 2009. Throughout the subsequent study, articles 5 to 10 of Decree-Law no. 72/2008 and the previous conflicts of law rules repealed by it, as well as the provisions established in Directives 88/357/CEE and 2002/83/CE on applicable law and those that have been introduced by Rome I Regulation shall be analyzed. Key words: Decree-Law no. 72/2008, Rome Convention, Rome I Regulation, Directive 88/357/CEE, Directive 2002/83/CE, Decree-Law no. 94-B/98, insurance contract, international insurance contract, applicable law, conflicts of law rules, conflicts law, risk, commitment, lois de police

Dielectric screening and plasmon resonances in bilayer graphene

The plasmon structure of intrinsic and extrinsic bilayer graphene is investigated in the framework of ab initio time-dependent density-functional theory (TDDFT) at the level of the random-phase approximation (RPA). A two-step scheme is adopted, where the electronic ground state of a periodically repeated slab of bilayer graphene is first determined with full inclusion of the anisotropic band structure and the interlayer interaction; a Dyson-like equation is then solved self-consistently in order to calculate the so-called density-response function of the many-electron system. A two-dimensional correction is subsequently applied in order to eliminate the artificial interaction between the replicas. The energy range below ∼30 eV is explored, focusing on the spectrum of single-particle excitations and plasmon resonances induced by external electrons or photons. The high-energy loss features of the π and σ+π plasmons, particularly their anisotropic dispersions, are predicted and discussed in relation with previous calculations and experiments performed on monolayer and bilayer graphene. At the low-energy end, the energy-loss function is found to be (i) very sensitive to the injected charge carrier density in doped bilayer graphene and (ii) highly anisotropic. Furthermore, various plasmon modes are predicted to exist and are analyzed with reference to the design of novel nanodevicesM.P. and M.G. acknowledge financial support by the European Commission, the European Social Fund, and the Regione Calabria, (POR) Calabria - FSE 2007/2013, and the hospitality of CIC nanoGUNE and the Donostia International Physics Center (DIPC). V.M.S. acknowledges the partial support from the Basque Departamento de Educación, UPV/EHU (Grant No. IT-756-13) and the Spanish Ministry of Economy and Competitiveness MINECO (Grant No. FIS2013-48286-C2-1-P

Imaging and Controlling Coherent Phonon Wave Packets in Single Graphene Nanoribbons

The motion of atoms is at the heart of any chemical or structural transformation in molecules and materials. Upon activation of this motion by an external source, several (usually many) vibrational modes can be coherently coupled, thus facilitating the chemical or structural phase transformation. These coherent dynamics occur on the ultrafast time scale, as revealed, e.g., by nonlocal ultrafast vibrational spectroscopic measurements in bulk molecular ensembles and solids. Tracking and controlling vibrational coherences locally at the atomic and molecular scales is, however, much more challenging and in fact has remained elusive so far. Here, we demonstrate that the vibrational coherences induced by broadband laser pulses on a single graphene nanoribbon (GNR) can be probed by femtosecond coherent anti-Stokes Raman spectroscopy (CARS) when performed in a scanning tunnelling microscope (STM). In addition to determining dephasing (~ 440 fs) and population decay times (~1.8 ps) of the generated phonon wave packets, we are able to track and control the corresponding quantum coherences, which we show to evolve on time scales as short as ~ 70 fs. We demonstrate that a two-dimensional frequency correlation spectrum unequivocally reveals the quantum couplings between different phonon modes in the GNR.Comment: 18 page

Preliminary Approach for a Prototype of Sustainable Antiseismic Dwelling in Nepal Based on the Historic Vernacular Tradition

The effects of the 2015 Gorkha earthquake in Nepal revealed deficiencies in the most recent vernacular architecture, which no longer uses wooden reinforcements due to national anti-deforestation laws. It also highlighted the shortcomings found in reinforced concrete architecture, which is generally scanty and poorly reinforced due to the high import cost of construction steel. The geography of Nepal has led to the development of a wide variety of vernacular architecture using local materials such as stone, brick or earth in the form of rammed earth and adobe walls [1]. Moreover, although its tradition in the construction of vaults is not as prominent as in neighbouring regions of India, Nepal has developed its own tradition in the construction of vaults and domes, which are generally self-supporting and made of brick or adobe with lime mortar. The design of a prototype of seismic house in Nepal aims to use a modular housing unit with rammed earth walls and/or walls made of materials recycled from previous earthquakes, as well as tile vaults with bamboo sleepers, and possibly vegetable fibre grids. These avoid the use of imported materials, favouring km0 and sustainable materials while following local tradition. Several potential housing units have undergone linear seismic analysis on finite element models, with variations in planimetric layout and the types of tile vault, from the simpler barrel vault to the sail vault. Both are analysed searching for the best shape in terms of seismic efficiency, evaluating stress and strain state. The results obtained from this preliminary study clearly show that, under seismic actions, the response from the construction system using depressed sail vaults and rammed earth walls with bamboo reinforcements is more efficient and homogeneous in terms of tension and deformation. This is due to the geometric symmetry which determines the same response in several directions, unlike vaults with a characteristically strong directionality (barrel vault). The seismic response of the prototype described is examined by assessing the influence in terms of thrust and deformation of bamboo reinforcements inside the walls. For this, laboratory tests are used to identify the mechanical characteristics of bamboo to be employed in the finite element modelling and calculation, as the values found in the literature vary depending on the physical and chemical characteristics of the material. This study therefore proposes a more sustainable architectural model with greater antiseismic resistance, always in keeping with local constructive tradition