Loaded TEM cell versus free space: comparison of the E-fieldsinside dielectric spherical objects

A Crawford (1974) cell is a convenient tool for generating transverse electromagnetic fields. In this work, a dielectric hemisphere is assumed to be placed on the central septum of a Crawford cell; the field inside the hemisphere is numerically evaluated and then compared with that inside the corresponding sphere in free-space (illuminated by a plane wave) for which the analytical solution is known     

Prerequisites between learning objects: Automatic extraction based on a machine learning approach

One standing problem in the area of web-based e-learning is how to support instructional designers to effectively and efficiently retrieve learning materials, appropriate for their educational purposes. Learning materials can be retrieved from structured repositories, such as repositories of Learning Objects and Massive Open Online Courses; they could also come from unstructured sources, such as web hypertext pages. Platforms for distance education often implement algorithms for recommending specific educational resources and personalized learning paths to students. But choosing and sequencing the adequate learning materials to build adaptive courses may reveal to be quite a challenging task.In particular, establishing the prerequisite relationships among learning objects, in terms of prior requirements needed to understand and complete before making use of the subsequent contents, is a crucial step for faculty, instructional designers or automated systems whose goal is to adapt existing learning objects to delivery in new distance courses. Nevertheless, this information is often missing. In this paper, an innovative machine learning-based approach for the identification of prerequisites between text-based resources is proposed. A feature selection methodology allows us to consider the attributes that are most relevant to the predictive modeling problem. These features are extracted from both the input material and weak-taxonomies available on the web. Input data undergoes a Natural language process that makes finding patterns of interest more easy for the applied automated analysis. Finally, the prerequisite identification is cast to a binary statistical classification task. The accuracy of the approach is validated by means of experimental evaluations on real online coursers covering different subjects.     

Towards automated wide area visual surveillance: tracking objects between spatially-separated, uncalibrated views

This paper presents a solution to the problem of tracking intermittent targets that can overcome long-term occlusions, as well as movement between camera views. Unlike other approaches, our system does not require topological knowledge of the site or labelled training patterns during the learning period. The approach uses the statistical consistency of data obtained automatically over an extended period of time rather than explicit geometric calibration to automatically learn the salient reappearance periods for objects. This allows us to predict where objects may reappear, and within how long. We demonstrate how these salient reappearance periods can be used with a model of physical appearance to track objects between spatially separate regions in single and separated views.     

Switching between different conformers of a molecule: Multilevel memory elements

We report voltage-driven electrical bistability in an organic semiconductor, namely Ponceau SS. Conductance switching to different levels or “multilevel switching” in devices based on thin-films is due to different density of high-conducting molecules. In a monolayer of Ponceau SS, we have observed one low-conducting and two high-conducting states. This is due to three configurable planes of the molecule exhibiting at least two stable high-conducting conformers. Apart from establishing conductance switching to be a molecular phenomenon, the multilevel conductance in a monolayer shows that a single molecule can exhibit multilevel memory application.     

The Portuguese urban system: An opposition between its hierarchical organization in cyberspace vs. physical space

The advent of computer and information technologies during the past decades, and their widespread use, is radically transforming the dynamics of communication and our understanding of spatial relationships. This empirical analysis intends to question how this kind of technological changes affect past trends in urban and regional development, specifically if they have enough potential to generate substantial adjustments on traditional Portuguese urban hierarchy, or instead, if it is an unexpected contribute to reinforce territorial disintegration tendencies. We analyse some geographic measurements of Internet ownership, especially the density of .pt domains and the presence of each Portuguese city in the most used web search engines, in order to verify the plasticity of space throughout Portugal by the growing use of information and communication technologies (ICTs), and the ways it has been stretched or compressed. The findings of this study suggest that the role of ICTs in the struggle against spatial inequalities in Portugal is less relevant than expected.     

Intraction between tracheal sound and flow rate: a comparison ofsome different flow evaluations from lung sounds

We simultaneously recorded tracheal sound and air flow from nine normal subjects (seven males and two females). Sound was picked up at the supra sternal notch with an air-coupled sensitive microphone held in a small airtight probe. Flow was measured at the mouth using a pneumotachograph Fleisch n degrees 2. Both sound and flow were directly digitized at a sampling rate of 5120 Hz and then divided in 128-sample blocks. For each sound block the frequency spectrum was computed using the fast Fourier transform. In order to evaluate instantaneous flow-rate from tracheal sounds we investigated eight methods divided in two groups of four. In the first group (i.e., reference curves methods), we assumed that a relationship existed between sound and flow and was thus reflected by the variations of certain parameters. We chose to use simple straightforward relationships, already known and published. We tested four different parameters. During a calibration phase, we built for each parameter P a reference curve representing the variations of P versus flow and being specific to each subject. Then, an unknown flow was evaluated in calculating P on a 128-sample block, and the reference curve gave the corresponding flow. In the second group, we made a hierarchial clustering analysis of sound spectra for revealing the frequency modifications, induced by the flow. We tested two kinds of spectra as well as two ways of associating a flow to a given cluster. This led us to four other methods for calculating the flow. All the eight methods but one gave a mean uncertainty in the measure of flow of about 15%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal power fluctuations of amorphous silicon thin‐film solar modules: distinguishing between different contributions

Several works report on seasonal fluctuations of power production of amorphous silicon (a‐Si). These oscillations are due to two overlapping phenomena (i) spectral and (ii) the Staebler–Wronski effects. It is hence difficult to assess—for a given location and climatic conditions—which one has the largest impact. By means of a straightforward approach based on two sets of single‐junction a‐Si photovoltaic modules (stored indoors/exposed outdoors) and on two different I–V measurement set‐ups (indoor and outdoor), we were able to separate the different contributions to this phenomenon. For the test‐site of Lugano, seasonal oscillations account for performance variations of a‐Si of ~10% (±5% around an annual average value with a minimum around the mid of January and a maximum around mid‐July). The time‐phase of the overall effect lies in between that of the two distinguished phenomena. (i) Spectral variations seem to have the highest impact on the outdoor performance of a‐Si with an amplitude corresponding to 10.5% (± ~5.2%). Moreover, the influence of spectral variations on the outdoor performance of a‐Si (and for comparison of c‐Si) was modeled, and the experimental data were found to be in excellent agreement with the theoretical simulation; (ii) the Staebler–Wronski effect has a slightly lower influence with an amplitude of ~8% (±4% with a minimum at the middle of February and a maximum around mid‐August). Because of the position (46°N) and average climatic conditions (southern Alpine climate) of Lugano, these observations are possibly representative of a large part of continental Europe. Copyright © 2012 John Wiley & Sons, Ltd.