Overview of coded light projection techniques for automatic 3D profiling

Obtaining automatic 3D profile of objects is one of the most important issues in computer vision. With this information, a large number of applications become feasible: from visual inspection of industrial parts to 3D reconstruction of the environment for mobile robots. In order to achieve 3D data, range finders can be used. Coded structured light approach is one of the most widely used techniques to retrieve 3D information of an unknown surface. An overview of the existing techniques as well as a new classification of patterns for structured light sensors is presented. This kind of systems belong to the group of active triangulation method, which are based on projecting a light pattern and imaging the illuminated scene from one or more points of view. Since the patterns are coded, correspondences between points of the image(s) and points of the projected pattern can be easily found. Once correspondences are found, a classical triangulation strategy between camera(s) and projector device leads to the reconstruction of the surface. Advantages and constraints of the different patterns are discussed

University teacher competences in a virtual teaching/learning environment : analysis of a teacher training experience

This paper attempts to shed light on the competencies a teacher must have inorder to teach in online university environments. We will relate a teacher trainingexperience, which was designed taking into account the methodological criteriaestablished in line with previous theoretical principles. The main objective of ouranalysis is to identify the achievements and difficulties of a specific formativeexperience, with the ultimate goal of assessing the suitability of this conceptualmethodologicalframework for the design of formative proposals aiming to contribute tothe development of teacher competencies for virtual environments.

Assessing the structural change of strategic mobility: determinants under hypercompetitive environments

The primary purpose of this exploratory empirical study is to examine the structural stability of a limited number of alternative explanatory factors of strategic change. On the basis of theoretical arguments and prior empirical evidence from two traditional perspectives, we propose an original empirical framework to analyse whether these potential explanatory factors have remained stable over time in a highly turbulent environment. This original question is explored in a particular setting: the population of Spanish private banks. The firms of this industry have experienced a high level of strategic mobility as a consequence of fundamental changes undergone in their environmental conditions over the last two decades (mainly changes related to the new banking and financial regulation process). Our results consistently support that the effect of most explanatory factors of strategic mobility considered did not remain stable over the whole period of analysis. From this point of view, the study sheds new light on major debates and dilemmas in the field of strategy regarding why firms change their competitive patterns over time and, hence, to what extent the "contextdependency" of alternative views of strategic change as their relative validation can vary over time for a given population. Methodologically, this research makes two major contributions to the study of potential determinants of strategic change. First, the definition and measurement of strategic change employing a new grouping method, the Model-based Cluster Method or MCLUST. Second, in order to asses the possible effect of determinants of strategic mobility we have controlled the non-observable heterogeneity using logistic regression models for panel data.

Environment conditions and biological innovations in the european agrarian growth, 1819-1939

The circumstances that were the driving forces behind Europe's economic growth beginning in the 19th century are diverse, and not easily prioritized. Until the 1970's, specifically, in Economy and Economic History, attention was focused on different institutional and technological variables, and various regularities were proposed. Nevertheless, new studies also underlined that the evolution of economic activity could not be understood considering only the new production possibilities offered by market economies. As a result, today it is also accepted that those processes can not be explained without considering two additional circumstances: the energy flows that sustained them, and the changes undergone in their transformation In this context, a question arises that takes on special importance. Which was the influence of the biological change in the economic growth?. A part of the flows of energy must be made into food, and this transformation can only happen with the participation.

Tomato response to a high light transmission greenhouse film

Increasing greenhouse light transmission has a positive effect not only in Northern latitudes but in Mediterranean countries as well. A greenhouse, H2, with a tetrafluoroethylene copolymer 60 microns film, (Asahi Glass company, Aflex) characterised by its high light transmission and durability was compared to another greenhouse with a co-extruded film considered as a control, H1. Tomato crop response to the increase in light during winter and summer with high temperature and light was evaluated. Light transmission in H2 remained very high in spite of the observed dust accumulation and the low angle of incidence of the winter solar radiation. Transmissivity was clearly higher for H2 (81 to 83 % throughout the season) than in the control (around 63 %). The rest of the climatic parameters were similar in both greenhouses, either in the winter or in the summer evaluations. In spite of the high solar radiation in H2, the summer temperature could be maintained at the desired levels by using evaporative cooling. Accumulated tomato yield and quality was better in the H2 greenhouse (15 % more for the winter crop and 27% more for the summer crop). Fruit size was bigger in the winter crop. As an overall conclusion, the use of high light transmissive films in Mediterranean areas is very convenient for many vegetable crops. This is valid not only in winter but in summer, provided the greenhouse has good ventilation or evaporative cooling to overcome the increase in sensible heat caused by this increase in light..

Continuity of set-valued maps revisited in the light of tame geometry

Continuity of set-valued maps is hereby revisited: after recalling some basic concepts of variational analysis and a short description of the State-of-the-Art, we obtain as by-product two Sard type results concerning local minima of scalar and vector valued functions. Our main result though, is inscribed in the framework of tame geometry, stating that a closed-valued semialgebraic set-valued map is almost everywhere continuous (in both topological and measure-theoretic sense). The result –depending on stratification techniques– holds true in a more general setting of o-minimal (or tame) set-valued maps. Some applications are briefly discussed at the end.

Development of an optimized methodology for tensile testing of carbon steels in hydrogen environment

The study was performed at OCAS, the Steel Research Centre of ArcelorMittal for the Industry market. The major aim of this research was to obtain an optimized tensile testing methodology with in-situ H-charging to reveal the hydrogen embrittlement in various high strength steels. The second aim of this study has been the mechanical characterization of the hydrogen effect on hight strength carbon steels with varying microstructure, i.e. ferrite-martensite and ferrite-bainite grades. The optimal parameters for H-charging - which influence the tensile test results (sample geometry type of electrolyte, charging methods effect of steel type, etc.) - were defined and applied to Slow Strain Rate testing, Incremental Step Loading and Constant Load Testing. To better understand the initiation and propagation of cracks during tensile testing with in-situ H-charging, and to make the correlation with crystallographic orientation, some materials have been analyzed in the SEM in combination with the EBSD technique. The introduction of a notch on the tensile samples permits to reach a significantly improved reproducibility of the results. Comparing the various steel grades reveals that Dual Phase (ferrite-martensite) steels are more sensitive to hydrogen induced cracking than the FB (ferritic-bainitic) ones. This higher sensitivity to hydrogen was found back in the reduced failure times, increased creep rates and enhanced crack initiation (SEM) for the Dual Phase steels in comparison with the FB steels.

TwHistory : Sharing History Using Twitter

In light of the fact that several studies indicate that students can benefit from deeper understandings of the processes by which historical accounts are constructed, history educators have increasingly been focused on finding ways to teach students how to read and reason about events in the same manner as professional historians (Wineburg, 2001; Spoehr & Spoehr, 1994; Hynd, Holschuh, & Hubbard, 2004; Wiley & Voss, 1996). One possible resource for supporting this development may come out of emerging web-based technologies. New technologies and increased access to historical records and artifacts posted the Internet may be precisely the tools that can help students (Bass, Rosenzweig, & Mason, 1999). Given the right context, we believe it is possible to combine such resources and tools to create an environment for students that could strengthen their abilities to read and reason about historical events. Moreover, we believe that social media, specifically, microblogging (Nardi, Schiano, Gumbrecht, & Swartz, 2004) could play a key role.

What should a virtual University Library environment look like?

Over the past year, the Open University of Catalonia library has been designing its new website with this question in mind. Our main concern has been how to integrate the library in the student day to day study routine to not to be only a satellite tool. We present the design of the website that, in a virtual library like ours, it is not only a website but the whole library itself. The central point of the web is my library, a space that associates the library resources with the student's curriculum and their course subjects. There the students can save the resources as favourites, comment or share them. They have also access to all the services the library offers them. The resources are imported from multiple tools such as Millennium, SFX, Metalib and Dspace to the Drupal CMS. Then the resources' metadata can be enriched with other contextual information from other sources, for example the course subjects. And finally they can be exported in standard, open data formats making them available for linked data applications.

Escriptura de la tesi doctoral, benestar i context d'aprenentatge: Un estudi des de les percepcions dels doctorands

Les representacions que els estudiants es fan sobre les tasques acadèmiques són cabdals per entendre com les desenvolupen. Creiem que això no és una excepció en estudiants de doctorat amb les seves tesis i és per això que en aquesta recerca estem interessats en investigar com els estudiants entenen els estudis de doctorat. La literatura revisada preocupada per l’experiència del doctorat, és a dir, com els doctorands perceben aquest procés, se centra en variables de benestar, context d’aprenentatge i escriptura. Amb el propòsit d’obtenir un quadre complert sobre com els doctorands entenen fer una tesi, 627 doctorands han completat El Qüestionari de l’Experiència Doctoral (Lonka i altres, 2007) que hem procedit a adaptar a la població espanyola. Aquest instrument mesura les tres variables esmentades (al llarg de 49 enunciats de resposta Likert) i de forma general algunes qüestions del procés doctoral (8 preguntes de resposta oberta) que complementen/donen llum a la interpretació de les dades quantitatives. A més, es demana informació del context del doctorand (18 preguntes) que ajuda a entendre millor el desenvolupament de la tesi en cada cas. Donat que algunes dificultats que els estudiants manifesten en el doctorat tenen a veure amb la percepció de no disposar d’estratègies suficients per regular el procés d’escriptura, ens hem plantejat recollir dades més específiques en relació a l’escriptura de la tesi entrevistant 10 doctorands per separat i posteriorment junts en un focus grup. Pensem que la nostra investigació pot contribuir en la reflexió de la qualitat dels programes de doctorat ja que creiem que els estudiants tenen molt a dir i que cal escoltar les seves veus. A més, si els tutors disposen d’informació sobre com els seus alumnes viuen els estudis de doctorat, segurament entendran millor com porten a terme les seves tesis i podran oferir-los ajudes més ajustades.

Vision-based localization of an underwater robot in a structured environment

This paper presents a vision-based localization approach for an underwater robot in a structured environment. The system is based on a coded pattern placed on the bottom of a water tank and an onboard down looking camera. Main features are, absolute and map-based localization, landmark detection and tracking, and real-time computation (12.5 Hz). The proposed system provides three-dimensional position and orientation of the vehicle along with its velocity. Accuracy of the drift-free estimates is very high, allowing them to be used as feedback measures of a velocity-based low-level controller. The paper details the localization algorithm, by showing some graphical results, and the accuracy of the system

On the way to solve lighting problems in underwater imaging

A major obstacle to processing images of the ocean floor comes from the absorption and scattering effects of the light in the aquatic environment. Due to the absorption of the natural light, underwater vehicles often require artificial light sources attached to them to provide the adequate illumination. Unfortunately, these flashlights tend to illuminate the scene in a nonuniform fashion, and, as the vehicle moves, induce shadows in the scene. For this reason, the first step towards application of standard computer vision techniques to underwater imaging requires dealing first with these lighting problems. This paper analyses and compares existing methodologies to deal with low-contrast, nonuniform illumination in underwater image sequences. The reviewed techniques include: (i) study of the illumination-reflectance model, (ii) local histogram equalization, (iii) homomorphic filtering, and, (iv) subtraction of the illumination field. Several experiments on real data have been conducted to compare the different approaches

Calibration of a Structured Light-Based Stereo Catadioptric Sensor

Catadioptric sensors are combinations of mirrors and lenses made in order to obtain a wide field of view. In this paper we propose a new sensor that has omnidirectional viewing ability and it also provides depth information about the nearby surrounding. The sensor is based on a conventional camera coupled with a laser emitter and two hyperbolic mirrors. Mathematical formulation and precise specifications of the intrinsic and extrinsic parameters of the sensor are discussed. Our approach overcomes limitations of the existing omni-directional sensors and eventually leads to reduced costs of production

An approach to visual servoing based on coded light

Positioning a robot with respect to objects by using data provided by a camera is a well known technique called visual servoing. In order to perform a task, the object must exhibit visual features which can be extracted from different points of view. Then, visual servoing is object-dependent as it depends on the object appearance. Therefore, performing the positioning task is not possible in presence of non-textured objects or objects for which extracting visual features is too complex or too costly. This paper proposes a solution to tackle this limitation inherent to the current visual servoing techniques. Our proposal is based on the coded structured light approach as a reliable and fast way to solve the correspondence problem. In this case, a coded light pattern is projected providing robust visual features independently of the object appearance