Design of dual-reflector antennas with arbitrary phase and amplitude distributions

A synthesis method based on geometrical optics for designing a dual-reflector antenna system with an arbitrary phase and amplitude distribution in the aperture of the second reflector is presented. The first reflector may be illuminated by a pattern with an arbitrarily curved phase front. A pair of first-order ordinary nonlinear differential equations of the formdy/dx=f(x, y)are developed for the system. Questions concerning uniqueness, existence and bounds for the solutions can be answered. Calculations and numerical results for the design of a uniform amplitude and phase dual-reflector system are presented.     

Control architecture for human-robot integration: application to a robotic wheelchair.

Completely autonomous performance of a mobile robot within noncontrolled and dynamic environments is not possible yet due to different reasons including environment uncertainty, sensor/software robustness, limited robotic abilities, etc. But in assistant applications in which a human is always present, she/he can make up for the lack of robot autonomy by helping it when needed. In this paper, the authors propose human-robot integration as a mechanism to augment/improve the robot autonomy in daily scenarios. Through the human-robot-integration concept, the authors take a further step in the typical human-robot relation, since they consider her/him as a constituent part of the human-robot system, which takes full advantage of the sum of their abilities. In order to materialize this human integration into the system, they present a control architecture, called architecture for human-robot integration, which enables her/him from a high decisional level, i.e., deliberating a plan, to a physical low level, i.e., opening a door. The presented control architecture has been implemented to test the human-robot integration on a real robotic application. In particular, several real experiences have been conducted on a robotic wheelchair aimed to provide mobility to elderly people.     

Thermodynamic analysis of steel deoxidization processes during tapping and refining operations

A thermodynamic model based on the interaction parameter approach for molten metal solutions and a quasi‐chemical model for molten slags and non‐metallic inclusions was employed to analyze steel deoxidization during tapping and refining operations in a ladle furnace. This model is able to predict the mineralogical nature of non‐metallic inclusions and their amount through thermodynamics and mass balances. It was found that the addition sequence of deoxidizers during a tapping procedure influences the nature and amount of the different inclusions. Besides, the metal‐slag equilibrium is readily reached after tapping and at the end of steel treatment in the ladle furnace. The model proved to be useful for steel cleanliness assessments and the design of steel deoxidization practices.     

A randomized experiment comparing random and cutoff-based assignment.

In this article, we review past studies comparing randomized experiments to regression discontinuity designs, mostly finding similar results, but with significant exceptions. The latter might be due to potential confounds of study characteristics with assignment method or with failure to estimate the same parameter over methods. In this study, we correct the problems by randomly assigning 588 participants to be in a randomized experiment or a regression discontinuity design in which they are otherwise treated identically, comparing results estimating both the same and different parameters. Analysis includes parametric, semiparametric, and nonparametric methods of modeling nonlinearities. Results suggest that estimates from regression discontinuity designs approximate the results of randomized experiments reasonably well but also raise the issue of what constitutes agreement between the 2 estimates. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A LEGO Mindstorms NXT approach for teaching at Data Acquisition,Control Systems Engineering and Real-Time Systems undergraduate courses

LEGO Mindstorms NXT robots are being increasingly used in undergraduate courses, mostly in robotics-related subjects. But other engineering topics, like the ones found in data acquisition, control and real-time subjects, also have difficult concepts that can be well understood only with good lab exercises. Such exercises require physical educational tools that should be low cost, easy to configure and use, multi-purpose and motivational for the students, being all of this hard to achieve with a single device. The “classical” solution has been to acquire specific commercial kits for each subject, or even topic, usually proprietary and expensive. Our work extends the already existing alternative of using the LEGO Mindstorms NXT robots as a training platform, but not by imitating the same approach of commercial kits (e.g., to isolate some part of the robot for teaching a particular topic); we rather aim at accomplishing all the mentioned requirements simultaneously. For that purpose, we have used only one out-of-the-box, complete robot configuration, to be shared among different subjects without hardware/software/firmware modifications. This has reduced significantly the effort of a group of professors when preparing exercises, and encouraged the reuse of their work among several topics and subjects. Also, we have collected a number of surveys on students and the professors' experiences. In this paper we describe our approach and present in detail the results, which assess the higher motivational adequacy of using a complete robot in these subjects and also the real fulfillment of the other requirements along several academic years.     

Testing variability-intensive systems using automated analysis: an application to Android

Software product lines are used to develop a set of software products that, while being different, share a common set of features. Feature models are used as a compact representation of all the products (e.g., possible configurations) of the product line. The number of products that a feature model encodes may grow exponentially with the number of features. This increases the cost of testing the products within a product line. Some proposals deal with this problem by reducing the testing space using different techniques. However, a daunting challenge is to explore how the cost and value of test cases can be modeled and optimized in order to have lower-cost testing processes. In this paper, we present TESting vAriAbiLity Intensive Systems (TESALIA), an approach that uses automated analysis of feature models to optimize the testing of variability-intensive systems. We model test value and cost as feature attributes, and then we use a constraint satisfaction solver to prune, prioritize and package product line tests complementing prior work in the software product line testing literature. A prototype implementation of TESALIA is used for validation in an Android example showing the benefits of maximizing the mobile market share (the value function) while meeting a budgetary constraint.     

An XPS and ellipsometry study of Cr-O-Al mixed oxides grown by reactive magnetron sputtering

Cr-O-Al thin film mixed oxides grown on Si (100) substrates by reactive magnetron sputtering using different target compositions from 90% Cr (10% Al) to 10% Cr (90% Al) and oxygen fluxes in the range from 0 to 15 sccm have been investigated using ex situ XPS, XPS depth profiles and ARXPS. The chemical information obtained with XPS as well as the observed chemical shift of the Cr 2p, Al 2s and O 1s bands points to the formation of mixed substitutional Me₂O₃ oxides (Me = Al + Cr) instead of the formation of single oxide phases. Compositions and stoichiometries obtained from concentration depth profile measurements (CDP) simultaneously using XPS and Ar⁺ bombardment confirm the formation of such a type of substitutional mixed oxides. ARXPS allows ruling out oxygen preferential sputtering during Ar⁺ bombardment. Finally, it is shown that the optical properties of the films like their refractive index can be controlled through their chemical composition.     

Calculation of integrated intensities in aberration-corrected Z-contrast images

Inclusion of spatial incoherence has been shown to give quantitative agreement between non-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images and theoretical simulations. Here we show that, using the same approach, a significant improvement in the correlation between calculated and experimental normalized integrated intensities is obtained in the InAsP ternary semiconductor alloy, but residual discrepancies remain. We have demonstrated, in good agreement with experimental intensities obtained in calibrated samples, that normalized integrated intensities show a low dependence on the sample thickness over a wide range of thickness values. This behaviour does not occur in conventional (non-aberration-corrected) images and constitutes a powerful tool for straightforward interpretation of high-resolution images in terms of atomic column-resolved compositional maps.