Semiconducting chains of gold and silver

The authors introduce a geometry for ultrathin Au and Ag wires that ab initio calculations indicate to be more stable than previously considered planar geometries for these systems, by about 0.1 eV per atom. This structure is insulating for both metals and for related Ag_(0.5)-Au_(0.5) alloys, with gaps of 1.3 eV for Au, 0.8 eV for Ag, and varying between 0.1 eV and 1.9 eV for the alloys. The insulating nature of the geometry is not a result of Peierls instabilities, and is analyzed in terms of an interplay between geometric and electronic structure effects.Comment: 4 pages, 3 figures (3 pages in published format

Berry-phase treatment of the homogeneous electric field perturbation in insulators

A perturbation theory of the static response of insulating crystals to homogeneous electric fields, that combines the modern theory of polarization (MTP) with the variation-perturbation framework is developed, at unrestricted order of perturbation. First, we address conceptual issues related to the definition of such a perturbative approach. In particular, in our definition of an electric-field-dependent energy functional for periodic systems, the position operator appearing in the perturbation term is replaced by a Berry-phase expression, along the lines of the MTP. Moreover, due to the unbound nature of the perturbation, a regularization of the Berry-phase expression for the polarization is needed in order to define a numerically-stable variational procedure. Regularization is achieved by means of discretization, which can be performed either before or after the perturbation expansion. We compare the two possibilities and apply them to a model tight-binding Hamiltonian. Lowest-order as well as generic formulas are presented for the derivatives of the total energy, the normalization condition, the eigenequation, and the Lagrange parameters.Comment: 52 pages + 4 figures; accepted for publication in Physical Review

Surface dangling bond states and band-lineups in hydrogen-terminated Si, Ge, and Ge/Si nanowires

We report an ab initio study of the electronic properties of surface dangling-bond (SDB) states in hydrogen-terminated Si and Ge nanowires with diameters between 1 and 2 nm, Ge/Si nanowire heterostructures, and Si and Ge (111) surfaces. We find that the charge transition levels e(+/-) of SDB states behave as a common energy reference among Si and Ge wires and Si/Ge heterostructures, at 4.3 +/- 0.1 eV below the vacuum level. Calculations of e(+/-) for isolated atoms indicate that this nearly constant value is a periodic-table atomic property.Comment: 4 pages, 5 figures, two-column forma

THE role of the technology acceptance model in information systems research: a case study

Explaining the factors that lead to use and acceptance of information technology (IT), both at individual and organizational levels, has been the focus of information systems (IS) researchers since 1970s. The Technology Acceptance Model (TAM) is known as such an explanatory model and has increasingly gained recognition due to its focus on theories of human behaviour. Although this model has faced with some criticism in terms of not being able to fully explain the social-technical acceptance of technology, it is still known as one of the best IS methodologies that contributes greatly to explaining it. This paper discusses, describes and explains TAM as one of the well-known information system research methodologies and attempts to demonstrate how this model can be applied in practice in IS research projects. TAM is widely used in different areas of IS studies such as e-commerce, e-business, multimedia and mobile commerce. This paper shows how TAM can be applied in an IS research project by referring to a case study conducted in the area of mobile banking in the UK. This paper aims to contribute to IS research by providing an informed criticism of TAM as well as a clear proposal on how to use it

Complex evolution of the electronic structure from polycrystalline to monocrystalline graphene: generation of a new Dirac point

First principles calculations, employed to address the properties of polycrystalline graphene, indicate that the electronic structure of tilt grain boundaries in this system displays a rather complex evolution towards graphene bulk, as the tilt angle decreases, with the generation of a new Dirac point at the Fermi level, and an anisotropic Dirac cone of low energy excitations. Moreover, the usual Dirac point at the {\bf K} point falls below the Fermi level, and rises towards it as the tilt angle decreases. Further, our calculations indicate that the grain-boundary formation energy behaves non-monotonically with the tilt angle, due to a change in the the spatial distribution and relative contributions of the bond-stretching and bond-bending deformations associated with the formation of the defect.Comment: 4 pages (+ a few references on 5th page). Contains text (.tex) file + 4 figures + pdf fil

Unclassified autoimmune pancreatitis mimicking pancreatic cancer

A 24-year-old black male presented with a 1-week obstructive jaundice and intermittent abdominal pain, with no significant weight loss and an unsuspicious abdominal exam. Blood chemistry showed a cholestatic pattern but a complete immunological and tumoral panel (anti-smooth muscle antibody, anti-mitochondrial antibody, anti-nuclear antibody, anti-neutrophil cytoplasmic antibody, anti-Smith, anti-double-stranded-DNA antibody (anti-dsDNA), complement C3/C4, carcinoembryonic antigen, CA 19-9 and IgG4) were all within normal limits. Abdominal ultrasound revealed dilatation of the intra and extra-hepatic bile ducts. CT scan showed an abnormal dilatation of the distal bile duct but no focal enlargement of the head of the pancreas. Endoscopic ultrasound suggested an inflammatory process but the magnetic resonance cholangio-pancreatography favored a neoplastic obstruction of the distal common bile duct. Fine-needle aspiration cytology was insufficient for definitive diagnosis and the patient underwent major surgery. Follow-up with mild exocrine pancreatic insufficiency treated with enzyme replacement.info:eu-repo/semantics/publishedVersio

Operation and maintenance in ST-MA

This paper will review the Operation & Maintenance (O&M) activities in the ST-MA group, giving an overview of the services provided by the Group as well as the contract activities. As an introduction, a conceptual framework for O&M is proposed in order to better situate the domains of Operation and Maintenance respectively. The ST-MA activities shall be looked at through the three main service axes and special emphasis will be given to the contractual implementation, supervision and follow-up methodology

Living will

RESUMO Este artigo resulta de uma reflexão bioética sobre o Testamento Vital e a sua origem, com desenvolvimento de conceitos como a autonomia e o consentimento informado. Entendendo-se que a Bioética tem hoje um enorme potencial nas democracias plurais, a reflexão sobre os valores éticos poderá contribuir significativamente para as escolhas de uma sociedade que, mais esclarecida, poderá estabelecer melhor as prioridades em saúde, numa lógica de implementação que poderá ser mais favorável às gerações vindouras. ABSTRACT This article results from a bioethical reflection on Living Will and its origins, while adressing concepts such as autonomy and informed consent. Understanding that bioethics has a huge potential in plural democracies, the reflection on ethical values may contribute significantly to the choices any society will have to make because it will be more enlightened and therefore will be able to establish better priorities in healthcare, following a logic implementation that may be more favourable to future generations