Generator coherency and area detection in large power systems

This paper provides a new general approach for defining coherent generators in power systems based on the coherency in low frequency inter-area modes. The disturbance is considered to be distributed in the network by applying random load changes which is the random walk representation of real loads instead of a single fault and coherent generators are obtained by spectrum analysis of the generators velocity variations. In order to find the coherent areas and their borders in the inter-connected networks, non-generating buses are assigned to each group of coherent generator using similar coherency detection techniques. The method is evaluated on two test systems and coherent generators and areas are obtained for different operating points to provide a more accurate grouping approach which is valid across a range of realistic operating points of the system.

Single-cell force spectroscopy, an emerging tool to quantify cell adhesion to biomaterials

Cell adhesion receptors play a central role in sensing and integrating signals provided by the cellular environment. Thus, understanding adhesive interactions at the cell-biomaterial interface is essential to improve the design of implants that should emulate certain characteristics of the cell's natural environment. Numerous cell adhesion assays have been developed; among these, atomic force microscopy-based single-cell force spectroscopy (AFM-SCFS) provides a versatile tool to quantify cell adhesion at physiological conditions. Here we discuss how AFM-SCFS can be used to quantify the adhesion of living cells to biomaterials and give examples of using AFM-SCFS in tissue engineering and regenerative medicine. We anticipate that in the near future, AFM-SCFS will be established in the biomaterial field as an important technique to quantify cell-biomaterial interactions and thereby will contribute to the optimization of implants, scaffolds, and medical devices.

On the effect of Reynolds number for flow past three side-by-side square cylinders for unequal gap spacings

Flow patterns and aerodynamic characteristics behind three side-by-side square cylinders has been found depending upon the unequal gap spacing (g1 = s1/d and g2 = s2/d) between the three cylinders and the Reynolds number (Re) using the Lattice Boltzmann method. The effect of Reynolds numbers on the flow behind three cylinders are numerically studied for 75 ≤ Re ≤ 175 and chosen unequal gap spacings such as (g1, g2) = (1.5, 1), (3, 4) and (7, 6). We also investigate the effect of g2 while keeping g1 fixed for Re = 150. It is found that a Reynolds number have a strong effect on the flow at small unequal gap spacing (g1, g2) = (1.5, 1.0). It is also found that the secondary cylinder interaction frequency significantly contributes for unequal gap spacing for all chosen Reynolds numbers. It is observed that at intermediate unequal gap spacing (g1, g2) = (3, 4) the primary vortex shedding frequency plays a major role and the effect of secondary cylinder interaction frequencies almost disappear. Some vortices merge near the exit and as a result small modulation found in drag and lift coefficients. This means that with the increase in the Reynolds numbers and unequal gap spacing shows weakens wakes interaction between the cylinders. At large unequal gap spacing (g1, g2) = (7, 6) the flow is fully periodic and no small modulation found in drag and lift coefficients signals. It is found that the jet flows for unequal gap spacing strongly influenced the wake interaction by varying the Reynolds number. These unequal gap spacing separate wake patterns for different Reynolds numbers: flip-flopping, in-phase and anti-phase modulation synchronized, in-phase and anti-phase synchronized. It is also observed that in case of equal gap spacing between the cylinders the effect of gap spacing is stronger than the Reynolds number. On the other hand, in case of unequal gap spacing between the cylinders the wake patterns strongly depends on both unequal gap spacing and Reynolds number. The vorticity contour visualization, time history analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and force statistics are systematically discussed for all chosen unequal gap spacings and Reynolds numbers to fully understand this valuable and practical problem.

Analysis of primary user duty cycle impact on spectrum sensing performance

Spectrum sensing is considered to be one of the most important tasks in cognitive radio. Many sensing detectors have been proposed in the literature, with the common assumption that the primary user is either fully present or completely absent within the window of observation. In reality, there are scenarios where the primary user signal only occupies a fraction of the observed window. This paper aims to analyse the effect of the primary user duty cycle on spectrum sensing performance through the analysis of a few common detectors. Simulations show that the probability of detection degrades severely with reduced duty cycle regardless of the detection method. Furthermore we show that reducing the duty cycle has a greater degradation on performance than lowering the signal strength.

Analysis of detection performance in spectrum sensing optimisation for long sensing periods

Spectrum sensing optimisation techniques maximise the efficiency of spectrum sensing while satisfying a number of constraints. Many optimisation models consider the possibility of the primary user changing activity state during the secondary user's transmission period. However, most ignore the possibility of activity change during the sensing period. The observed primary user signal during sensing can exhibit a duty cycle which has been shown to severely degrade detection performance. This paper shows that (a) the probability of state change during sensing cannot be neglected and (b) the true detection performance obtained when incorporating the duty cycle of the primary user signal can deviate significantly from the results expected with the assumption of no such duty cycle.

Incongruence between self-reported and observed senior physical education teaching styles : an analysis using Mosston and Ashworth’s spectrum

Pedagogical styles, methods, models, practices or strategies are valued for what they claim they can achieve. In recent times curriculum documents and governments have called for a range of teaching approaches to meet the variety of learner differences and allow students to make more independent decision making in physical education (Hardy and Mawer, 1999). One well known system of categorizing teaching styles is the Mosston and Ashworth’s Spectrum of Teaching Styles (2002). In Queensland, prior to 2005, no research had been conducted on the teaching styles used by teachers of Physical Education. However, many teachers self-reported that they employed a variety of teaching styles depending on the aims and content of the material to be taught (Cothran, et al., 2005). This research, for the first time, collected teacher’s self-reported use of teaching styles and through observations verify the styles that were being used to teach Senior Physical Education in Queensland. More specifically the aims of the research were to determine: a) What teaching styles teachers of Senior Physical Education in Queensland believe they use? i) Were they using a range of teaching styles? ii) Were teachers of Senior Physical Education in Queensland using teaching styles that the Queensland Senior Physical Education Syllabus (2004) required? b) If Mosston and Ashworth’s (2002) Spectrum of Teaching Styles were used to categorise styles observed during the teaching of Senior Physical Education did the styles being used provide opportunities for evaluating as described by the Queensland Senior Physical Education Syllabus (2004)? The research was conducted in two phases. Part A involved use of a questionnaire to determine the teaching styles Queensland teachers of Senior Physical Education reported using and how often they reported using them. The questionnaire was administered to 110 teachers throughout Queensland. The sample was determined from 346 schools teaching Senior Physical Education (in 2006) across the state of Queensland, Australia. 286 questionnaires were sent to 77 non-randomised schools. There were 66 male and 44 female respondents in the sample. A wide range of teaching styles were reportedly used by teachers of Senior Physical Education with Practice Style-Style B, Command Style-Style A and Divergent Discovery Style-Style H, the most reportedly used. The Self-Teaching Style-Style K was reportedly used the least by teachers involved in this study. From the respondents a group of teachers were identified to form the participants for Part B. Part B of the study involved observation of a group of volunteer participants (from those who had completed the questionnaire) who displayed many of the ‘typical’ characteristics, and a cross-section of backgrounds, of teachers of Senior Physical Education in Queensland. In the case of this study, the criteria used to select the group of teachers to be observed teaching were, teaching experience (number of years: 0-4, 5-10 and 11 years and over), gender, geographical location of schools (focused on Brisbane and near area for travel/access purposes), profile of the students at schools (girls, boys or co-educational), nature of school (Government or Private) and the physical activities being taught in a school (activities to reflect all the areas of physical activity outlined within the syllabus). A total of 27 questionnaire respondents from Part A indicated that they were willing to be observed teaching practical lessons. The respondents who volunteered to be involved in Part B of the study came from different regions across the state of Queensland and was not confined to the Brisbane metropolitan area or large cities. From the group of people who volunteered for Part B four came from outside Brisbane and 23 from the Brisbane area. The final observation group of nine participants included eight teachers from the Brisbane area and one from a rural area. The characteristics of the final group included three females and six males from private and public schools with a range of teaching experience in years and a range of physical activities. Four year 12 and five year 11 teachers and their classes were videoed on three occasions as they progressed through an eight – nine week unit of work. This resulted in 24 hours 48 minutes and 20 seconds (or 4465 observations) of video teaching data which was subsequently coded by several researchers (99% interobserver reliability) to determine the teaching styles employed by the participants. This research indicated that, based on Mosston and Ashworth’s (2002) Spectrum of Teaching Styles, teachers of Senior Physical Education in Queensland used predominantly one style to teach 27 observed lessons. This is in sharp contrast to the variety of styles 110 teachers self- reportedly used and in spite of the Queensland Senior Physical Education Syllabus (2004) suggesting a range of specific styles be used. These results are discussed in the context of the Queensland Senior Physical Education Syllabus (2004), teacher knowledge of teaching styles and high-stakes curriculum and external pressures such as national testing and the publication of data from schools in tabloid newspapers. The data and findings in this research provide a rationale for improving teacher knowledge regarding teaching styles and the need for a clear definition of terminology in syllabus documents. Careful examination of the effects that the publishing of school data may have on teaching styles is advised. This research not only collected teacher’s perceptions of the teaching styles they believed they used it also verified these claims through direct observations of the teachers while teaching. These findings are relevant to syllabus writers, teacher educators, policy makers within education and teachers.

Inducing shades of meaning by matrix methods : a first step towards thematic analysis of opinion

This article explores two matrix methods to induce the ``shades of meaning" (SoM) of a word. A matrix representation of a word is computed from a corpus of traces based on the given word. Non-negative Matrix Factorisation (NMF) and Singular Value Decomposition (SVD) compute a set of vectors corresponding to a potential shade of meaning. The two methods were evaluated based on loss of conditional entropy with respect to two sets of manually tagged data. One set reflects concepts generally appearing in text, and the second set comprises words used for investigations into word sense disambiguation. Results show that for NMF consistently outperforms SVD for inducing both SoM of general concepts as well as word senses. The problem of inducing the shades of meaning of a word is more subtle than that of word sense induction and hence relevant to thematic analysis of opinion where nuances of opinion can arise.