Nonlinear stability of <i>E</i> centers in Si_1-<i>x</i>Ge_<i>x</i>: electronic structure calculations

Electronic structure calculations are used to investigate the binding energies of defect pairs composed of lattice vacancies and phosphorus or arsenic atoms (E centers) in silicon-germanium alloys. To describe the local environment surrounding the E center we have generated special quasirandom structures that represent random silicon-germanium alloys. It is predicted that the stability of E centers does not vary linearly with the composition of the silicon-germanium alloy. Interestingly, we predict that the nonlinear behavior does not depend on the donor atom of the E center but only on the host lattice. The impact on diffusion properties is discussed in view of recent experimental and theoretical results

Intrinsic and extrinsic diffusion of indium in germanium

Diffusion experiments with indium (In) in germanium (Ge) were performed in the temperature range between 550 and 900°C. Intrinsic and extrinsic doping levels were achieved by utilizing various implantation doses. Indium concentration profiles were recorded by means of secondary ion mass spectrometry and spreading resistance profiling. The observed concentration independent diffusion profiles are accurately described based on the vacancy mechanism with a singly negatively charged mobile In-vacancy complex. In accord with the experiment, the diffusion model predicts an effective In diffusion coefficient under extrinsic conditions that is a factor of 2 higher than under intrinsic conditions. The temperature dependence of intrinsic In diffusion yields an activation enthalpy of 3.51 eV and confirms earlier results of Dorner et al. [Z. Metallk. 73, 325 (1982)]. The value clearly exceeds the activation enthalpy of Ge self- diffusion and indicates that the attractive interaction between In and a vacancy does not extend to third nearest neighbor sites which confirms recent theoretical calculations. At low temperatures and high doping levels, the In profiles show an extended tail that could reflect an enhanced diffusion at the beginning of the annealing

Towards the fabrication of phosphorus qubits for a silicon quantum computer

The quest to build a quantum computer has been inspired by the recognition of the formidable computational power such a device could offer. In particular silicon-based proposals, using the nuclear or electron spin of dopants as qubits, are attractive due to the long spin relaxation times involved, their scalability, and the ease of integration with existing silicon technology. Fabrication of such devices however requires atomic scale manipulation - an immense technological challenge. We demonstrate that it is possible to fabricate an atomically-precise linear array of single phosphorus bearing molecules on a silicon surface with the required dimensions for the fabrication of a silicon-based quantum computer. We also discuss strategies for the encapsulation of these phosphorus atoms by subsequent silicon crystal growth.Comment: To Appear in Phys. Rev. B Rapid Comm. 5 pages, 5 color figure

Imobilização da lacase de Oudemansiella canarii: parâmetros cinéticos e reúso.

Neste trabalho, uma lacase de Oudemansiella canarii foi imobilizada pela técnica de agregados de enzimas reticuladas (CLEA). A imobilização foi eficiente com um rendimento de imobilização de 95% e retenção de atividade de 66,7%.Publicado no Anais Eletrônico da Galoá Proceddings

An all silicon quantum computer

A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are Si-29 nuclear spins arranged as chains in a Si-28 (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for readout. This proposal takes advantage of many of the successful aspects of solution NMR quantum computation, including ensemble measurement, RF control, and long decoherence times, but it allows for more qubits and improved initialization.Comment: ReVTeX 4, 5 pages, 2 figure

Can programme theory be used as a 'translational tool’ to optimise health service delivery in a national early years’ initiative in Scotland: a case study

Background Theory-based evaluation (TBE) approaches are heralded as supporting formative evaluation by facilitating increased use of evaluative findings to guide programme improvement. It is essential that learning from programme implementation is better used to improve delivery and to inform other initiatives, if interventions are to be as effective as they have the potential to be. Nonetheless, few studies describe formative feedback methods, or report direct instrumental use of findings resulting from TBE. This paper uses the case of Scotland’s, National Health Service, early years’, oral health improvement initiative (Childsmile) to describe the use of TBE as a framework for providing feedback on delivery to programme staff and to assess its impact on programmatic action.&lt;p&gt;&lt;/p&gt; Methods In-depth, semi-structured interviews and focus groups with key stakeholders explored perceived deviations between the Childsmile programme 'as delivered’ and its Programme Theory (PT). The data was thematically analysed using constant comparative methods. Findings were shared with key programme stakeholders and discussions around likely impact and necessary actions were facilitated by the authors. Documentary review and ongoing observations of programme meetings were undertaken to assess the extent to which learning was acted upon.&lt;p&gt;&lt;/p&gt; Results On the whole, the activities documented in Childsmile’s PT were implemented as intended. This paper purposefully focuses on those activities where variation in delivery was evident. Differences resulted from the stage of roll-out reached and the flexibility given to individual NHS boards to tailor local implementation. Some adaptations were thought to have diverged from the central features of Childsmile’s PT, to the extent that there was a risk to achieving outcomes. The methods employed prompted national service improvement action, and proposals for local action by individual NHS boards to address this.&lt;p&gt;&lt;/p&gt; Conclusions The TBE approach provided a platform, to direct attention to areas of risk within a national health initiative, and to agree which intervention components were 'core’ to its hypothesised success. The study demonstrates that PT can be used as a 'translational tool’ to facilitate instrumental use of evaluative findings to optimise implementation within a complex health improvement programme.&lt;p&gt;&lt;/p&gt

The UN in the lab

We consider two alternatives to inaction for governments combating terrorism, which we term Defense and Prevention. Defense consists of investing in resources that reduce the impact of an attack, and generates a negative externality to other governments, making their countries a more attractive objective for terrorists. In contrast, Prevention, which consists of investing in resources that reduce the ability of the terrorist organization to mount an attack, creates a positive externality by reducing the overall threat of terrorism for all. This interaction is captured using a simple 3×3 “Nested Prisoner’s Dilemma” game, with a single Nash equilibrium where both countries choose Defense. Due to the structure of this interaction, countries can benefit from coordination of policy choices, and international institutions (such as the UN) can be utilized to facilitate coordination by implementing agreements to share the burden of Prevention. We introduce an institution that implements a burden-sharing policy for Prevention, and investigate experimentally whether subjects coordinate on a cooperative strategy more frequently under different levels of cost sharing. In all treatments, burden sharing leaves the Prisoner’s Dilemma structure and Nash equilibrium of the game unchanged. We compare three levels of burden sharing to a baseline in a between-subjects design, and find that burden sharing generates a non-linear effect on the choice of the efficient Prevention strategy and overall performance. Only an institution supporting a high level of mandatory burden sharing generates a significant improvement in the use of the Prevention strategy