Phonon-mediated thermal conductance of mesoscopic wires with rough edges

We present an analysis of acoustic phonon propagation through long, free-standing, insulating wires with rough surfaces. Due to a crossover from ballistic propagation of the lowest-frequency phonon mode at $\omega <\omega _{1}=\pi c/W$ to a diffusive (or even localized) behavior upon the increase of phonon frequency, followed by re-entrance into the quasi-ballistic regime, the heat conductance of a wire acquires an intermediate tendency to saturate within the temperature range $T\sim \hbar \omega_{1}/k_{B}$.Comment: 4 pages, 3 figures included; minor changes and corrections, figures 1 and 2 replaced by better versions; to appear in PRB Brief Report

Feshbach resonances and mesoscopic phase separation near a quantum critical point in multiband FeAs-based superconductors

High Tc superconductivity in FeAs-based multilayers (pnictides), evading temperature decoherence effects in a quantum condensate, is assigned to a Feshbach resonance (called also shape resonance) in the exchange-like interband pairing. The resonance is switched on by tuning the chemical potential at an electronic topological transition (ETT) near a band edge, where the Fermi surface topology of one of the subbands changes from 1D to 2D topology. We show that the tuning is realized by changing i) the misfit strain between the superconducting planes and the spacers ii) the charge density and iii) the disorder. The system is at the verge of a catastrophe i.e. near a structural and magnetic phase transition associated with the stripes (analogous to the 1/8 stripe phase in cuprates) order to disorder phase transition. Fine tuning of both the chemical potential and the disorder pushes the critical temperature Ts of this phase transition to zero giving a quantum critical point. Here the quantum lattice and magnetic fluctuations promote the Feshbach resonance of the exchange-like anisotropic pairing. This superconducting phase that resists to the attacks of temperature is shown to be controlled by the interplay of the hopping energy between stripes and the quantum fluctuations. The superconducting gaps in the multiple Fermi surface spots reported by the recent ARPES experiment of D. V. Evtushinsky et al. arXiv:0809.4455 are shown to support the Feshbach scenario.Comment: 31 pages, 7 figure

Magnetic properties of irradiated quasi 2D type II superconductors

Persistent scaling behavior of magnetization in layered high Tc superconductors with short-range columnar defects is explained within the Ginzburg-Landau theory. In the weak field region, the scaling function differs from that of a clean sample and the critical temperature is renormalized due to defects. In the strong field region, defects are effectively suppressed and the scaling function, as well as the critical temperature are the same as in a clean superconductor. This picture is consistent with recent experimental results

Coordination and management of information for construction design projects - a framework for Portugal

In the construction industry in Portugal, the coordination and management of information for construction design projects has been neglected. The use of classification systems and protocols for the communication of information amongst the different stakeholders is poor and inefficient. This research aims to explore the viability of developing a systematic approach to the coordination of information amongst the multiple project stakeholders in the Portuguese Construction Industry. Bearing this in mind, the core research question of this doctoral thesis is: What sort of framework and guidelines are needed for the successful implementation of a classification information system for construction project design data in Portugal, which is accessible to all stakeholders involved? A mixed methods approach was developed for this purpose, with emphasis given to qualitative research techniques. Methods used comprised: literature review, quantitative survey, semi-structured interviews and focus group discussions. Whereas quantitative research methods contributed to a more rigorous interpretation process, qualitative research methods offered a solid description of the former. This methodology was used in order to establish and design a conceptual classification framework model for information coordination and management throughout the design project and construction in Portugal. First, constraints and enablers to framework development and implementation were identified at all levels: political, cultural and behaviour, legal, technical and educational, economic and financial, and organizational issues. Three overarching issues were also identified: corruption, lack of accountability and non-compliance timelines/deadlines. Then, a conceptual framework was developed, detailing 1) content, 2) characteristics of an environment conductive to a successful development, implementation and use of the framework, and 3) guidelines to its dissemination