Theory of one and two donors in Silicon

We provide here a roadmap for modeling silicon nano-devices with one or two group V donors (D). We discuss systems containing one or two electrons, that is, D^0, D^-, D_2^+ and D_2^0 centers. The impact of different levels of approximation is discussed. The most accurate instances -- for which we provide quantitative results -- are within multivalley effective mass including the central cell correction and a configuration interaction account of the electron-electron correlations. We also derive insightful, yet less accurate, analytical approximations and discuss their validity and limitations -- in particular, for a donor pair, we discuss the single orbital LCAO method, the Huckel approximation and the Hubbard model. Finally we discuss the connection between these results and recent experiments on few dopant devices.Comment: 13 pages, 6 figure

Impact of the valley degree of freedom on the control of donor electrons near a Si/SiO_2 interface

We analyze the valley composition of one electron bound to a shallow donor close to a Si/barrier interface as a function of an applied electric field. A full six-valley effective mass model Hamiltonian is adopted. For low fields, the electron ground state is essentially confined at the donor. At high fields the ground state is such that the electron is drawn to the interface, leaving the donor practically ionized. Valley splitting at the interface occurs due to the valley-orbit coupling, V_vo^I = |V_vo^I| e^{i theta}. At intermediate electric fields, close to a characteristic shuttling field, the electron states may constitute hybridized states with valley compositions different from the donor and the interface ground states. The full spectrum of energy levels shows crossings and anti-crossings as the field varies. The degree of level repulsion, thus the width of the anti-crossing gap, depends on the relative valley compositions, which vary with |V_vo^I|, theta and the interface-donor distance. We focus on the valley configurations of the states involved in the donor-interface tunneling process, given by the anti-crossing of the three lowest eigenstates. A sequence of two anti-crossings takes place and the complex phase theta affects the symmetries of the eigenstates and level anti-crossing gaps. We discuss the implications of our results on the practical manipulation of donor electrons in Si nanostructures.Comment: 8 pages, including 5 figures. v2: Minor clarifying changes in the text and figures. Change of title. As published in PR

Component-based programming for higher-order attribute grammars

This paper presents techniques for a component-based style of programming in the context of higher-oder attribute grammars (HAG). Attribute grammar components are "plugged in" into larger attribute grammar systems through higher-order attribute grammars. Higher-order attributes are used as (intermediate) "gluing" data structures.This paper also presents two attribute grammar components that can be re-used across different language-based tool specifications: a visualizer and animator of programs and a graphical user interface AG component. Both components are reused in the definition of a simple language processor. The techniques presented in this paper are implemented in LRC: a purely functional, higher-order attribute grammar-based system that generates language-based tools.(undefined

PUDENDAL NERVE BLOCK AND OBSTETRIC SIMULATION

A primeira descrição do bloqueio do nervo pudendo foi em 1908. Esta é uma técnica indicada para analgesia nas fases mais adiantadas do trabalho de parto. O uso de técnicas analgésicas eficazes desde os estadios mais precoces do trabalho de parto, como as técnicas do neuro-eixo, deixaram o bloqueio do pudendo para segundo plano. No entanto, é de fácil execução, habitualmente pelo obstetra, e com baixo risco de hemorragia ou infeção. O bloqueio do pudendo é um procedimento com poucas oportunidades de treino na prática clínica, pelo que o retomar da prática na sua execução através do uso de simuladores obstétricos torna-se pertinente. Ainda, a sua utilização em cenários simulados permite a familiarização de equipas multidisciplinares na sua aplicação em diversos contextos, emergentes ou não emergentes. Os principais objetivos deste trabalho são (1) efetuar uma revisão sobre o bloqueio do nervo pudendo na analgesia de parto, focando as principais vantagens e limitações, (2) repensar a sua utilização na ausência ou contraindicação de outras técnicas analgésicas, (3) reavivar a técnica de execução através da simulação aplicada à Obstetrícia

Improving count rate capability of timing RPCs by increasing the detector working temperature

This communication describes test beam results, focusing on detection efficiency and timing precision, of common float glass timing Resistive Plate Chambers (tRPCs) exposed to a $2.7$~GeV proton beam and operated at above ambient temperature in order to increase the count rate capability of the chambers, by exploiting the reduction in the resistivity of the glass electrodes. Results suggest that the count rate capability can be extended at least up to $1500~Hz/cm^2$ when the detector is operated at $40.6^{\circ}$C without noticeable loss of efficiency or timing precision degradation with values of $90\%$ and $100$~ps, respectively, for this specific timing RPC arrangement.Comment: to be published in Proceedings of 15th Pisa Meeting on Advanced Detector

Quasi-one-dimensional system as a high-temperature superconductor

It is well-known that quasi-one-dimensional superconductors suffer from the pairing fluctuations that significantly reduce the superconducting temperature or even completely suppress any coherent behavior. Here we demonstrate that a coupling to a robust pair condensate changes the situation dramatically. In this case the quasi-one-dimensional system can be a high temperature superconductor governed by the proximity to the Lifshitz transition at which the Fermi level approaches the lower edge of the single-particle spectrum.Comment: 5 pages, 1 figur

Physical mechanisms of interface-mediated intervalley coupling in Si

The conduction band degeneracy in Si is detrimental to quantum computing based on spin qubits, for which a nondegenerate ground orbital state is desirable. This degeneracy is lifted at an interface with an insulator as the spatially abrupt change in the conduction band minimum leads to intervalley scattering. We present a theoretical study of the interface-induced valley splitting in Si that provides simple criteria for optimal fabrication parameters to maximize this splitting. Our work emphasizes the relevance of different interface-related properties to the valley splitting.Comment: 4 pages, revised versio