Particle Creation by a Moving Boundary with Robin Boundary Condition

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic moving boundary. We derive a Bogoliubov transformation between input and output bosonic field operators, which allows us to calculate the spectral distribution of created particles. The cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases. These two limits yield the same spectrum, which turns out to be an upper bound for the spectra derived for Robin BC. We show that the particle emission effect can be considerably reduced (with respect to the Dirichlet/Neumann case) by selecting a particular value for the oscillation frequency of the boundary position

Duality and interval analysis over idempotent semirings

In this paper semirings with an idempotent addition are considered. These algebraic structures are endowed with a partial order. This allows to consider residuated maps to solve systems of inequalities $A \otimes X \preceq B$. The purpose of this paper is to consider a dual product, denoted $\odot$, and the dual residuation of matrices, in order to solve the following inequality $A \otimes X \preceq X \preceq B \odot X$. Sufficient conditions ensuring the existence of a non-linear projector in the solution set are proposed. The results are extended to semirings of intervals

Quantum radiation in a plane cavity with moving mirrors

We consider the electromagnetic vacuum field inside a perfect plane cavity with moving mirrors, in the nonrelativistic approximation. We show that low frequency photons are generated in pairs that satisfy simple properties associated to the plane geometry. We calculate the photon generation rates for each polarization as functions of the mechanical frequency by two independent methods: on one hand from the analysis of the boundary conditions for moving mirrors and with the aid of Green functions; and on the other hand by an effective Hamiltonian approach. The angular and frequency spectra are discrete, and emission rates for each allowed angular direction are obtained. We discuss the dependence of the generation rates on the cavity length and show that the effect is enhanced for short cavity lengths. We also compute the dissipative force on the moving mirrors and show that it is related to the total radiated energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review

Compressive Phase Contrast Tomography

When x-rays penetrate soft matter, their phase changes more rapidly than their amplitude. In- terference effects visible with high brightness sources creates higher contrast, edge enhanced images. When the object is piecewise smooth (made of big blocks of a few components), such higher con- trast datasets have a sparse solution. We apply basis pursuit solvers to improve SNR, remove ring artifacts, reduce the number of views and radiation dose from phase contrast datasets collected at the Hard X-Ray Micro Tomography Beamline at the Advanced Light Source. We report a GPU code for the most computationally intensive task, the gridding and inverse gridding algorithm (non uniform sampled Fourier transform).Comment: 5 pages, "Image Reconstruction from Incomplete Data VI" conference 7800, SPIE Optical Engineering + Applications 1-5 August 2010 San Diego, CA United State

Google Glass as a learning tool: sharing evaluation results for the role of optical head mounted displays in education

This paper provides an overview of the findings from an evaluation of the role of Google Glass in education over the past three years. The authors have experimented with Optical Head Mounted Displays as a support tool for various learning activities over the past few years. The study described in the paper commenced back in 2014 and continued despite the fact that the development of the Google Glass technology was paused and then shifted towards enterprise clientele. This was a result of our confidence that the future of learning interfaces is aligned to the proliferation of augmented reality and the fact that the Google Glass interface offers an ideal tool for learners due to its light structure and seamless wearing experience. The paper discusses how Google Glass has been used for a range of learning activities and describes the learners’ experiences from using the device. The main contribution of the paper is in the form of measuring the success of the specific interface by sharing the results of three years of evaluations. The evaluation results are further analysed taking under consideration a number of profiling techniques of the learners involved including their personality type and learning style

Casimir torque between corrugated metallic plates

We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 $\mu{\rm m}.$Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding

The Symmetry Concept in the Perspective of Basic Education Teachers

The curricular changes that have occurred with the Portuguese Mathematics programme of study of 2007 showed, among other situations, the introduction of new contents and the new concept of symmetry. For the teachers, these changes require scientific updates to be provided so that the outcomes of the mathematics teaching can be guaranteed. In the academic year 2011/2012 a questionnaire was applied to a 142 inservice basic education teachers of a particular region of Portugal, to analyze the content knowledge in this subject (symmetry) and the form of scientific update occurred. The processing of data allowed us to identify inadequate conceptions, beliefs, topics more or less successful in responses and also compare the teacher’s responses of the different teaching groups.info:eu-repo/semantics/publishedVersio