Phase estimation for thermal Gaussian states

We give the optimal bounds on the phase-estimation precision for mixed Gaussian states in the single-copy and many-copy regimes. Specifically, we focus on displaced thermal and squeezed thermal states. We find that while for displaced thermal states an increase in temperature reduces the estimation fidelity, for squeezed thermal states a larger temperature can enhance the estimation fidelity. The many-copy optimal bounds are compared with the minimum variance achieved by three important single-shot measurement strategies. We show that the single-copy canonical phase measurement does not always attain the optimal bounds in the many-copy scenario. Adaptive homodyning schemes do attain the bounds for displaced thermal states, but for squeezed states they yield fidelities that are insensitive to temperature variations and are, therefore, sub-optimal. Finally, we find that heterodyne measurements perform very poorly for pure states but can attain the optimal bounds for sufficiently mixed states. We apply our results to investigate the influence of losses in an optical metrology experiment. In the presence of losses squeezed states cease to provide Heisenberg limited precision and their performance is close to that of coherent states with the same mean photon number.Comment: typos correcte

Phase separation in systems with absorbing states

We study the problem of phase separation in systems with a positive definite order parameter, and in particular, in systems with absorbing states. Owing to the presence of a single minimum in the free energy driving the relaxation kinetics, there are some basic properties differing from standard phase separation. We study analytically and numerically this class of systems; in particular we determine the phase diagram, the growth laws in one and two dimensions and the presence of scale invariance. Some applications are also discussed.Comment: Submitted to Europhysics Let

Synchronization in coupled map lattices as an interface depinning

We study an SOS model whose dynamics is inspired by recent studies of the synchronization transition in coupled map lattices (CML). The synchronization of CML is thus related with a depinning of interface from a binding wall. Critical behaviour of our SOS model depends on a specific form of binding (i.e., transition rates of the dynamics). For an exponentially decaying binding the depinning belongs to the directed percolation universality class. Other types of depinning, including the one with a line of critical points, are observed for a power-law binding.Comment: 4 pages, Phys.Rev.E (in press

Electronic and phononic properties of the chalcopyrite CuGaS2

The availability of ab initio electronic calculations and the concomitant techniques for deriving the corresponding lattice dynamics have been profusely used for calculating thermodynamic and vibrational properties of semiconductors, as well as their dependence on isotopic masses. The latter have been compared with experimental data for elemental and binary semiconductors with different isotopic compositions. Here we present theoretical and experimental data for several vibronic and thermodynamic properties of CuGa2, a canonical ternary semiconductor of the chalcopyrite family. Among these properties are the lattice parameters, the phonon dispersion relations and densities of states (projected on the Cu, Ga, and S constituents), the specific heat and the volume thermal expansion coefficient. The calculations were performed with the ABINIT and VASP codes within the LDA approximation for exchange and correlation and the results are compared with data obtained on samples with the natural isotope composition for Cu, Ga and S, as well as for isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev

Guidelines for oral assessment

En este documento se presentan los lineamientos y teoría para la implementación de un sistema de evaluación oral en el Centro de Idiomas de la Universidad Eafit. El texto desarrolla tres temas principales: 1) el enfoque comunicativo para la enseñanza y la evaluación ; 2) la planeación de la evaluación; y 3) el uso de las herramientas de evaluación.This document aims at offering teachers a framework for assessing oral language and some guidelines that will foster the implementation and practice of a homogeneous oral assessment system (OAS) at the EAFIT University Language Center. The document deals with three main topics, namely (1) Communicative Approach to Teaching and Assessment; (2) Planning for Assessment; and (3) Using the Oral Assessment Rubric

Nonequilibrium wetting

When a nonequilibrium growing interface in the presence of a wall is considered a nonequilibrium wetting transition may take place. This transition can be studied trough Langevin equations or discrete growth models. In the first case, the Kardar-Parisi-Zhang equation, which defines a very robust universality class for nonequilibrium moving interfaces, with a soft-wall potential is considered. While in the second, microscopic models, in the corresponding universality class, with evaporation and deposition of particles in the presence of hard-wall are studied. Equilibrium wetting is related to a particular case of the problem, it corresponds to the Edwards-Wilkinson equation with a potential in the continuum approach or to the fulfillment of detailed balance in the microscopic models. In this review we present the analytical and numerical methods used to investigate the problem and the very rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure

Estudio del comportamiento mecánico del hormigón de ultra- altas prestaciones (UHPC) reforzado con fibras híbridas y con consumo reducido de cemento

This article evaluated mechanical behavior of ultra-high performance concrete (UHPC) reinforced with hybrid steel and polypropylene fibers, with cement consumption of 250 kg/m³ and application of confining pressure in fresh state. The consistency of the mixture was analyzed, as well as mechanical properties of compressive strength, flexural strength and toughness. The percentages of hybridization were 50 to 100% of metal fibers and 0 to 50% of polypropylene fibers. Results showed that the compressive strength of the composite was 180 MPa (26100 psi), despite its low cement consumption of 250 kg/m³ (2.08 lb/gal), with 80% steel fibers and 20% polypropylene fibers. The combination of fibers increased the mixture’s toughness. For the composition with 80% steel fibers and 20% polypropylene fibers, the strength for large deformations increased by 191% compared with the mixture with 100% steel fibers, pointing out the benefits of hybridization.En este trabajo se evaluó el comportamiento mecánico de los hormigones de ultra-altas prestaciones (UHPC) reforzados con fibras híbridas de acero y polipropileno, con un consumo de cemento de 250 kg/m3 y aplicando una presión de confinamiento en su estado fresco. Se analizó la consistencia de la mezcla, las propiedades mecánicas de las resistencias a la compresión y flexión, así como la tenacidad. Se usaron porcentajes de hibridación del 50 al 100% de fibras metálicas y de 0 al 50% de fibras de polipropileno. Los resultados muestran que la resistencia a la compresión del compuesto fue de 180 MPa (26.100 psi), a pesar de su bajo consumo de cemento, de 250 kg/m³ (2,08 lb/gal), con 80% de fibras de acero y 20% de fibras de polipropileno. La combinación de fibras incrementó la tenacidad de la mezcla. Para esta misma composición, la resistencia para las grandes deformaciones aumentó en un 191% en comparación con la mezcla que contenía un 100% de fibras de acero, demostrando así los beneficios de la hibridación

Control and Model-Aided Inertial Navigation of a Nonholonomic Vehicle

International audienceThe present work deals with the control and localization problem of wheeled-mobile robots with nonholonomic constraints. In the proposed method a simple nonlinear control law, composed of a position and heading direction controller, is designed to asymptotically stabilize the position error. The control law takes into account the constraints on the control signals in order to avoid saturation of the actuators. Furthermore, this paper considers a method of using the dynamic vehicle model and vehicle's nonholonomic constraints in order to aid position and attitude estimates provided by an Inertial Navigation System (INS). It is shown that dynamic model and vehicle's nonholonomic constraints can reduce the error growth in robot position estimates. Simulations are included to confirm the effectiveness of the proposed scheme