Search results for: feedback stabilization

Authors: Nattawadee Sinpattanawong, Yaowaret Tharawoot

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This is an analytic and descriptive classroom-centered research, the purpose of which is to explore teacher verbal feedback on postgraduate students’ performances in presentations in English in an English for Specific Purposes (ESP) postgraduate classroom. The participants are a Thai female teacher, two Thai female postgraduate students, and two foreign male postgraduate students. The current study draws on both classroom observation and interview data. The class focused on the students’ presentations and the teacher’s providing verbal feedback on them was observed nine times with audio recording and taking notes. For the interviews, the teacher was interviewed about linkages between her verbal feedback and each student’s presentation skills in English. For the data analysis, the audio files from the observations were transcribed and analyzed both quantitatively and qualitatively. The quantitative approach addressed the frequencies and percentages of content of the teacher’s verbal feedback for each student’s performances based on eight presentation factors (content, structure, grammar, coherence, vocabulary, speaking skills, involving the audience, and self-presentation). Based on the quantitative data including the interview data, a qualitative analysis of the transcripts was made to describe the occurrences of several content of verbal feedback for each student’s presentation performances. The study’s findings may help teachers to reflect on their providing verbal feedback based on various students’ performances in presentation in English. They also help students who have similar characteristics to the students in the present study when giving a presentation in English improve their presentation performances by applying the teacher’s verbal feedback content.

Keywords: teacher verbal feedback, presentation factors, presentation in English, presentation performances

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Authors: E. Shahsavari, R. Ghasemi, A. Akramizadeh

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This paper presents a new method to design nonlinear feedback linearization controller for polymer electrolyte membrane fuel cells (PEMFCs). A nonlinear controller is designed based on nonlinear model to prolong the stack life of PEM fuel cells. Since it is known that large deviations between hydrogen and oxygen partial pressures can cause severe membrane damage in the fuel cell, feedback linearization is applied to the PEM fuel cell system so that the deviation can be kept as small as possible during disturbances or load variations. To obtain an accurate feedback linearization controller, tuning the linear parameters are always important. So in proposed study NSGA_II method was used to tune the designed controller in aim to decrease the controller tracking error. The simulation result showed that the proposed method tuned the controller efficiently.

Keywords: nonlinear dynamic model, polymer electrolyte membrane fuel cells, feedback linearization, optimal control, NSGA_II

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Authors: Omid Heydarnia, Akbar Allahverdizadeh, Behnam Dadashzadeh, M. R. Sayyed Noorani

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Underactuated biped robots control is one of the interesting topics in robotics. The main difficulties are its highly nonlinear dynamics, open-loop instability, and discrete event at the end of the gait. One of the methods to control underactuated systems is the partial feedback linearization, but it is not robust against uncertainties and disturbances that restrict its performance to control biped walking and running. In this paper, fuzzy partial feedback linearization is presented to overcome its drawback. Numerical simulations verify the effectiveness of the proposed method to generate stable and robust biped walking and running gaits.

Keywords: underactuated system, biped robot, fuzzy control, partial feedback linearization

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Authors: Jessica To

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Feedback is one of the powerful levers for enhancing students’ performance. However, some students are under-engaged with feedback because they lack responsibility for feedback uptake. To resolve this conundrum, recent literature proposes feedback partnerships in which students and teachers share the power and responsibilities to co-construct feedback. During feedback co-construction, students express feedback needs to teachers, and teachers respond to individuals’ needs in return. Though this approach can increase students’ feedback ownership, its application is lagging as the field lacks conceptual clarity and implementation guide. This presentation aims to discuss the conceptual framework of feedback partnerships and feedback co-construction strategies. It identifies the components of feedback partnerships and strategies which could facilitate feedback co-construction. A systematic literature review was conducted to answer the questions. The literature search was performed using ERIC, PsycINFO, and Google Scholar with the keywords “assessment partnership”, “student as partner,” and “feedback engagement”. No time limit was set for the search. The inclusion criteria encompassed (i) student-teacher partnerships in feedback, (ii) feedback engagement in higher education, (iii) peer-reviewed publications, and (iv) English as the language of publication. Those without addressing conceptual understanding and implementation strategies were excluded. Finally, 65 publications were identified and analysed using thematic analysis. For the procedure, the texts relating to the questions were first extracted. Then, codes were assigned to summarise the ideas of the texts. Upon subsuming similar codes into themes, four themes emerged: students’ responsibilities, teachers’ responsibilities, conditions for partnerships development, and strategies. Their interrelationships were examined iteratively for framework development. Establishing feedback partnerships required different responsibilities of students and teachers during feedback co-construction. Students needed to self-evaluate performance against task criteria, identify inadequacies and communicate their needs to teachers. During feedback exchanges, they interpreted teachers’ comments, generated self-feedback through reflection, and co-developed improvement plans with teachers. Teachers had to increase students’ understanding of criteria and evaluation skills and create opportunities for students’ expression of feedback needs. In feedback dialogue, teachers responded to students’ needs and advised on the improvement plans. Feedback partnerships would be best grounded in an environment with trust and psychological safety. Four strategies could facilitate feedback co-construction. First, students’ understanding of task criteria could be increased by rubrics explanation and exemplar analysis. Second, students could sharpen evaluation skills if they participated in peer review and received teacher feedback on the quality of peer feedback. Third, provision of self-evaluation checklists and prompts and teacher modeling of self-assessment process could aid students in articulating feedback needs. Fourth, the trust could be fostered when teachers explained the benefits of feedback co-construction, showed empathy, and provided personalised comments in dialogue. Some strategies were applied in interactive cover sheets in which students performed self-evaluation and made feedback requests on a cover sheet during assignment submission, followed by teachers’ response to individuals’ requests. The significance of this presentation lies in unpacking the conceptual framework of feedback partnerships and outlining feedback co-construction strategies. With a solid foundation in theory and practice, researchers and teachers could better enhance students’ engagement with feedback.

Keywords: conceptual framework, feedback co-construction, feedback partnerships, implementation strategies

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Authors: Saurav Bhattacharjee, Syam Nair

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Lime stabilization is a sustainable and economically viable option to address strength deficiencies of subgrade soils. However, exposure of stabilized layers to environmental elements can lead to a reduction in post stabilization strength gain expected in these layers. The current study investigates the impact of carbonation on strength properties of lime-treated soils. Manufactured soils prepared using varying proportions of bentonite silica mixtures was used in the study. Lime treated mixtures were exposed to different atmospheric conditions created by varying the concentrations of CO₂ in the testing chamber. Impact of CO₂ diffusion was identified based on changes in carbonate content and strength (UCS) properties. Changes in soil morphology were also investigated as part of the study. Rate of carbonation was observed to vary polynomially (2nd order) with exposure time. Strength properties of the mixes were observed to decrease with exposure time.

Keywords: carbonation, soil, stabilization, morphology

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Authors: Nattawadee Sinpattanawong

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Oral presentation has been used mostly in business communication. The business presentation is carrying out through an audio and visual presentation material such as statistical documents, projectors, etc. Common examples of business presentation are intra-organization and sales presentations. The study aims at investigating functions, strategies and contents of assessors’ verbal feedback on presenters’ oral presentations and exploring presenters’ learning process and specific views and expectations concerning assessors’ verbal feedback related to the delivery of the oral presentation. This study is designed as a descriptive qualitative research; four master students and one teacher in English for Business and Industry Presentation Techniques class of public university will be selected. The researcher hopes that any understanding how assessors’ verbal feedback on oral presentations and learning process may illuminate issues for other people. The data from this research may help to expand and facilitate the readers’ understanding of assessors’ verbal feedback on oral presentations and learning process in their own situations. The research instruments include an audio recorder, video recorder and an interview. The students will be interviewing in order to ask for their views and expectations concerning assessors’ verbal feedback related to the delivery of the oral presentation. After finishing data collection, the data will be analyzed and transcribed. The findings of this study are significant because it can provide presenters knowledge to enhance their learning process and provide teachers knowledge about providing verbal feedback on student’s oral presentations on a business context.

Keywords: business context, learning process, oral presentation, verbal feedback

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Authors: Y. Alrubyli

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Unmanned Arial Vehicles (UAVs), and more specifically, quadcopters need to be stable during their flights. Altitude stability is usually achieved by using a PID controller that is built into the flight controller software. Furthermore, the PID controller has gains that need to be tuned to reach optimal altitude stabilization during the quadcopter’s flight. For that, control system engineers need to tune those gains by using extensive modeling of the environment, which might change from one environment and condition to another. As quadcopters penetrate more sectors, from the military to the consumer sectors, they have been put into complex and challenging environments more than ever before. Hence, intelligent self-stabilizing quadcopters are needed to maneuver through those complex environments and situations. Here we show that by using online reinforcement learning with minimal background knowledge, the altitude stability of the quadcopter can be achieved using a model-free approach. We found that by using background knowledge instead of letting the online reinforcement learning algorithm wander for a while to tune the PID gains, altitude stabilization can be achieved faster. In addition, using this approach will accelerate development by avoiding extensive simulations before applying the PID gains to the real-world quadcopter. Our results demonstrate the possibility of using the trial and error approach of reinforcement learning combined with background knowledge to achieve faster quadcopter altitude stabilization in different environments and conditions.

Keywords: reinforcement learning, Q-leanring, online learning, PID tuning, unmanned aerial vehicle, quadcopter

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Authors: Nkiru I. Ibeakuzie, Paul D. J. Watson, John F. Pescatore

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In roadway construction, the cost of soil-cement stabilization per unit area is significantly influenced by the binder content, hence the need to optimise cement usage. This research work will characterize the influence of soil fractal geometry on properties of cement-stabilized soil, and strive to determine a correlation between mechanical proprieties of cement-stabilized soil and the mass fractal dimension Dₘ indicated by particle size distribution (PSD) of aggregate mixtures. Since strength development in cemented soil relies not only on cement content but also on soil PSD, this study will investigate the possibility of reducing cement content by changing the PSD of soil, without compromising on strength, reduced permeability, and compressibility. A series of soil aggregate mixes will be prepared in the laboratory. The mass fractal dimension Dₘ of each mix will be determined from sieve analysis data prior to stabilization with cement. Stabilized soil samples will be tested for strength, permeability, and compressibility.

Keywords: fractal dimension, particle size distribution, cement stabilization, cement content

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Authors: Debabrata Das

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This paper explains how to design a regulation loop for a power supply circuit. It also discusses the need of a regulation loop and the improvement of a circuit with regulation loop. A sample design is used to demonstrate how to use PSpice to design feedback loop to control output voltage of a power supply and how to check if the power supply is stable or oscillatory. A sample design is made using a specific Integrated Circuit (IC) available in the PSpice library. A designer can experiment feedback loop design using Cadence Pspice tool. PSpice is easy to use, reliable, and convenient. To test a feedback loop, generally, engineers use trial and error method with the hardware which takes a lot of time and manpower. Moreover, it is expensive because component and Printed Circuit Board (PCB) may go bad. PSpice can be used by designers to test their loop designs without using hardware circuits. A designer can save time, cost, manpower and simulate his/her power supply circuit accurately before making a real hardware using this software package.

Keywords: power electronics, feedback loop, regulation, stability, pole, zero, oscillation

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Authors: Sarah Kalaouze, Maxine Iannucelli, Kristen Dunfield

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Children’s implicit beliefs regarding intelligence (i.e., intelligence mindsets) influence their motivation, perseverance, and success. Previous research suggests that the way parents perceive failure influences the development of their child’s intelligence mindsets. We invited 151 children-parent dyads (Age= 5–6 years) to complete a series of difficult puzzles over zoom. We assessed parents’ intelligence and failure mindsets using questionnaires and recorded parents’ person/performance-oriented (e.g., “you are smart” or "you were almost able to complete that one) and process-oriented (e.g., “you are trying really hard” or "maybe if you place the bigger pieces first") failure feedback. We were interested in observing the relation between parental mindsets and the type of feedback provided. We found that parents’ intelligence mindsets were not predictive of the feedback they provided children. Failure mindsets, on the other hand, were predictive of failure feedback. Parents who view failure-as-debilitating provided more person-oriented feedback, focusing on performance and personal ability. Whereas parents who view failure-as-enhancing provided process-oriented feedback, focusing on effort and strategies. Taken all together, our results allow us to determine that although parents might already have a growth intelligence mindset, they don’t necessarily have a failure-as-enhancing mindset. Parents adopting a failure-as-enhancing mindset would influence their children to view failure as a learning opportunity, further promoting practice, effort, and perseverance during challenging tasks. The focus placed on a child’s learning, rather than their performance, encourages them to perceive intelligence as malleable (growth mindset) rather than fix (fixed mindset). This implies that parents should not only hold a growth mindset but thoroughly understand their role in the transmission of intelligence beliefs.

Keywords: mindset(s), failure, intelligence, parental feedback, parents

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Authors: Siti Nur Aida Mario, Farah Hafifee Ahmad, Rudy Tawie

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Soil Stabilization has been widely implemented in the construction industry nowadays. Peat soil is well known as one of the most problematic soil among the engineers. The procedures need to take into account both physical and engineering properties of the stabilized peat soil. This paper presents a result of plasticity index and hardening of treated peat soil with various dosage of additives. In order to determine plasticity of the treated peat soil, atterberg limit test which comprises plastic limit and liquid limit test has been conducted. Determination of liquid limit in this experimental study is by using cone penetrometer. Vicat testing apparatus has been used in the hardening test which the penetration of the plunger is recorded every one hour for 24 hours. The results show that the plasticity index of peat soil stabilized with 80% FAAC and 20% OPC has the lowest plasticity index and recorded the fastest initial setting time. The significant of this study is to promote greener solution for future soil stabilization industry.

Keywords: additives, hardening, peat soil, plasticity index, soil stabilization

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Authors: S. Vanker, A. Aaver, A. Roio, L. Nuut

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To be sure about the effective and less effective/ineffective approaches to course instruction, we hold the opinion that the faculty members need regular feedback from their students in order to be aware of how well or unwell their teaching styles have worked when instructing the courses. It can be confirmed without a slightest hesitation that undergraduate students’ motivated-ness can be sustained when continually improving the quality of teaching and properly sequencing the academic courses both, in the curricula and timetables. At Estonian Aviation Academy, four different forms of feedback are used: Lecture monitoring, questionnaires for all students, study information system subject monitoring and direct feedback received by the lecturer. Questionnaires for all students are arranged once during a study year and separately for the first year and senior students. The results are discussed in academic departments together with student representatives, analyzed with the teaching staff and, if needed, improvements are suggested. In addition, a monitoring system is planned where a lecturer acts in both roles – as an observer and as the lecturer. This will foster better exchange of experience and through this help to make the whole study process more interesting.

Keywords: learner motivation, feedback, student support, undergraduate education

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Authors: Ganesh Nandakumaran, Mehmet Karaata

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A wave is a distributed execution, often made up of a broadcast phase followed by a feedback phase, requiring the participation of all the system processes before a particular event called decision is taken. Wave algorithms with one initiator such as the 1-wave algorithm have been shown to be very efficient for broadcasting messages in tree networks. Extensions of this algorithm broadcasting a sequence of waves using a single initiator have been implemented in algorithms such as the m-wave algorithm. However as the network size increases, having a single initiator adversely affects the message delivery times to nodes further away from the initiator. As a remedy, broadcast waves can be allowed to be initiated by multiple initiator nodes distributed across the network to reduce the completion time of broadcasts. These waves initiated by one or more initiator processes form a collection of waves covering the entire network. Solutions to global-snapshots, distributed broadcast and various synchronization problems can be solved efficiently using waves with multiple concurrent initiators. In this paper, we propose the first stabilizing multi-wave sequence algorithm implementing waves started by multiple initiator processes such that every process in the network receives at least one sequence of broadcasts. Due to being stabilizing, the proposed algorithm can withstand transient faults and do not require initialization. We view a fault as a transient fault if it perturbs the configuration of the system but not its program.

Keywords: distributed computing, multi-node broadcast, propagation of information with feedback and cleaning (PFC), stabilization, wave algorithms

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Authors: Sameh A. S. Thabit Alariqi

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Food is widely packaged with plastic materials to prevent microbial contamination and spoilage. Ionizing radiation is widely used to sterilize the food-packaging materials. Sterilization by γ-radiation causes degradation for the plastic packaging materials such as embrittlement, stiffening, softening, discoloration, odour generation, and decrease in molecular weight. Many antioxidants can prevent γ-degradation but most of them are toxic. The migration of antioxidants to its environment gives rise to major concerns in case of food packaging plastics. In this attempt, we have aimed to utilize synergistic mixtures of stabilizers which are approved for food-contact applications. Ethylene-propylene-diene terpolymer (EPDM) have been melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer). Results were discussed by comparing the stabilizing efficiency of mixtures with and without phenol system. Among phenol containing systems where we mostly observed discoloration due to the oxidation of hindered phenol, the combination of secondary HAS, tertiary HAS, organo-phosphite and hindered phenol exhibited improved stabilization efficiency than single or binary additive systems. The mixture of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization. However, the combination of organo-phosphite with secondary HAS, tertiary HAS and phenol antioxidants have been found to give synergistic even at higher doses of -sterilization. The effects have been explained through the interaction between the stabilizers. After γ-irradiation, the consumption of oligomeric stabilizer significantly depends on the components of stabilization mixture. The effect of the organo-phosphite antioxidant on the overall stability has been discussed.

Keywords: ethylene-propylene-diene terpolymer, synergistic mixtures, gamma sterilization, gamma stabilization

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Authors: Ather Saeed, Arif Khan, Jeffrey Gosper

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Sensor devices are prone to errors and sudden node failures, which are difficult to detect in a timely manner when deployed in real-time, hazardous, large-scale harsh environments and in medical emergencies. Therefore, the loss of data can be life-threatening when the sensed phenomenon is not disseminated due to sudden node failure, battery depletion or temporary malfunctioning. We introduce a set of partial differential equations for localizing faults, similar to Green’s and Maxwell’s equations used in Electrostatics and Electromagnetism. We introduce a node organization and clustering scheme for self-stabilizing sensor networks. Green’s theorem is applied to regions where the curve is closed and continuously differentiable to ensure network connectivity. Experimental results show that the proposed GTFD (Green’s Theorem fault-detection and Self-stabilization) protocol not only detects faulty nodes but also accurately generates network stability graphs where urgent intervention is required for dynamically self-stabilizing the network.

Keywords: Green’s Theorem, self-stabilization, fault-localization, RSSI, WSN, clustering

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Authors: K. Senthil Kumar, A. Vasumalaikannan

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In this paper, teleoperation of the quadrotor using Internet with Force feedback is addressed. Teleoperation with Force feedback is the ability to remotely control a robot, where contact (obstacle) or environment (wind gust etc) information (force feedback) is communicated from the quadrotor to the master joystick and thus giving the operator a sense of telepresence. The stability and performance of such a teleoperator is highly dependent on the amount of time delay present in the control loop. This problem is further complicated given the fact that for network based communication the time delay is itself time varying and highly non deterministic. In this paper, a novel method using Neural based Smith Predictor at the master side the stability is achieved. The performance of the system even during worst case scenario is within acceptable.

Keywords: teleoperation, quadrotor, neural smith predictor, time delay

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Authors: Mohd. Khaidir Abu Talib, Noriyuki Yasufuku, Ryohei Ishikura

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It is well recognized that peat can impede the proper hydration of cement because of high organic content, presence of humic acid and less solid particles. That means the large amount of cement is required in order to neutralize the acids or otherwise the process of the peat stabilization remains retarded. Nevertheless, adding a great quantity of cement into the peat is absolutely an unfriendly and uneconomical solution. Sugarcane production is world number one commodities and produced a lot of bagasse. Bagasse is burnt to generate power required for diverse activities in the factory and leave bagasse ash as a waste. Increasing concern of disposal of bagasse residual creates interest to explore the potential application of this material. The objective of this study is to develop alternative binders that are environment friendly and contribute towards sustainable management by utilizing sugarcane bagasse ash (SCBA) in the stabilization of peat soil. Alongside SCBA, Ordinary Portland Cement (OPC), calcium chloride (CaCl2) and silica sand (K7) were used as additives to stabilize the peat that sampled from Hokkaido, Japan. In obtaining the optimal mix design, specimens of stabilized peat were tested in unconfined compression. It was found that stabilized peat comprising 20% and 5% (PCB1-20 and PCB2-5) partial replacement of OPC with SCBA 1 and SCBA 2 attain the maximum unconfined compressive strength (UCS) and discovered greater than untreated soil (P) and UCS of peat-cement (PC) specimen. At the optimal mix design, the UCS of the stabilized peat specimens increased with increasing of curing time, preloading during curing, OPC dosage and K7 dosage. For PCB1-20 mixture, inclusion of a minimum OPC dosage of 300 kg/m3 and K7 dosage of 500 kg/m3 along with curing under 20kPa pressure is recommendable for the peat stabilization to be effective. However for PCB2-5 mixture, it suggested to use more OPC and K7 dosage or alternatively increase the preloading during curing to 40kPa in order to achieve minimum strength target. It can be concluded that SCBA 1 has better quality than SCBA 2 in peat stabilization especially the contribution made by its fine particle size.

Keywords: peat stabilization, sugarcane bagasse ash utilization, partial cement replacement, unconfined strength

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Authors: Tomas Menard

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The synthesis of output-feedback control law has been investigated by many researchers since the last century. While many results exist for the case of Linear Time Invariant systems whose measurements are continuously available, nowadays, control laws are usually implemented on micro-controller, then the measurements are discrete-time by nature. This fact has to be taken into account explicitly in order to obtain a satisfactory behavior of the closed-loop system. One considers here a general class of systems corresponding to an observability normal form and which is subject to uncertainties in the dynamics and sampling of the output. Indeed, in practice, the modeling of the system is never perfect, this results in unknown uncertainties in the dynamics of the model. We propose here an output feedback algorithm which is based on a linear state feedback and a continuous-discrete time observer. The main feature of the proposed control law is that only discrete-time measurements of the output are needed. Furthermore, it is formally proven that the state of the closed loop system exponentially converges toward the origin despite the unknown uncertainties. Finally, the performances of this control scheme are illustrated with simulations.

Keywords: dynamical systems, output feedback control law, sampling, uncertain systems

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Authors: Musa Akdere, Gunnar Seide, Thomas Gries

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Carbon fibres are fibrous materials with a carbon atom amount of more than 90%. They combine excellent mechanicals properties with a very low density. Thus carbon fibre reinforced plastics (CFRP) are very often used in lightweight design and construction. The precursor material is usually polyacrylonitrile (PAN) based and wet-spun. During the production of carbon fibre, the precursor has to be stabilized thermally to withstand the high temperatures of up to 1500 °C which occur during carbonization. Even though carbon fibre has been used since the late 1970s in aerospace application, there is still no general method available to find the optimal production parameters and the trial-and-error approach is most often the only resolution. To have a much better insight into the process the chemical reactions during stabilization have to be analyzed particularly. Therefore, a model of the chemical reactions (cyclization, dehydration, and oxidation) based on the research of Dunham and Edie has been developed. With the presented model, it is possible to perform a complete simulation of the fibre undergoing all zones of stabilization. The fiber bundle is modeled as several circular fibers with a layer of air in-between. Two thermal mechanisms are considered to be the most important: the exothermic reactions inside the fiber and the convective heat transfer between the fiber and the air. The exothermic reactions inside the fibers are modeled as a heat source. Differential scanning calorimetry measurements have been performed to estimate the amount of heat of the reactions. To shorten the required time of a simulation, the number of fibers is decreased by similitude theory. Experiments were conducted to validate the simulation results of the fibre temperature during stabilization. The experiments for the validation were conducted on a pilot scale stabilization oven. To measure the fibre bundle temperature, a new measuring method is developed. The comparison of the results shows that the developed simulation model gives good approximations for the temperature profile of the fibre bundle during the stabilization process.

Keywords: carbon fibre, coupled simulation, exothermic reactions, fibre-air-interface

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Authors: J. Alvarez, J. Pimienta, R. Sarmiento

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Diode lasers working in free mode present different shifting and broadening determined by external factors such as temperature, current or mechanical vibrations, and they are not more useful in applications such as spectroscopy, metrology, and cooling of atoms, among others. Different configurations can reduce the spectral width of a laser; one of the most effective is to extend the optical resonator of the laser diode and use optical feedback either with the help of a partially reflective mirror or with a diffraction grating; this latter configuration is not only allowed to reduce the spectral width of the laser line but also to coarsely adjust its working wavelength, within a wide range typically ~ 10nm by slightly varying the angle of the diffraction grating. Two settings are commonly used for this purpose, the Littrow configuration and the Littmann Metcalf. In this paper, we present the design, construction, and characterization of a compact extended laser cavity in Littrow configuration. The designed cavity is compact and was machined on an aluminum block using computer numerical control (CNC); it has a mass of only 380 g. The design was tested on laser diodes with different wavelengths, 650nm, 780nm, and 795 nm, but can be equally efficient at other wavelengths. This report details the results obtained from the extended cavity working at a wavelength of 780 nm, with an output power of around 35mW and a line width of less than 1Mhz. The cavity was used to observe the spectrum of the corresponding Rubidium D2 line. By modulating the current and with the help of phase detection techniques, a dispersion signal with an excellent signal-to-noise ratio was generated that allowed the stabilization of the laser to a transition of the hyperfine structure of Rubidium with an integral proportional controller (PI) circuit made with precision operational amplifiers.

Keywords: Littrow, Littman-Metcalf, line width, laser stabilization, hyperfine structure

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Authors: Muhammad A. Alsubaie, Mubarak K. H. Alhajri, Tarek S. Altowaim

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A repetitive controller designed to accommodate periodic disturbances via state feedback is discussed. Periodic disturbances can be represented by a time delay model in a positive feedback loop acting on system output. A direct use of the small gain theorem solves the periodic disturbances problem via 1) isolating the delay model, 2) finding the overall system representation around the delay model and 3) designing a feedback controller that assures overall system stability and tracking error convergence. This paper addresses uncertainty conditions for the repetitive controller designed in state feedback in either past error feedforward or current error feedback using singular values. The uncertainty investigation is based on the overall system found and the stability condition associated with it; depending on the scheme used, to set an upper/lower limit weighting parameter. This creates a region that should not be exceeded in selecting the weighting parameter which in turns assures performance improvement against system uncertainty. Repetitive control problem can be described in lifted form. This allows the usage of singular values principle in setting the range for the weighting parameter selection. The Simulation results obtained show a tracking error convergence against dynamic system perturbation if the weighting parameter chosen is within the range obtained. Simulation results also show the advantage of weighting parameter usage compared to the case where it is omitted.

Keywords: model mismatch, repetitive control, singular values, state feedback

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Authors: Emmanuel Adu-Ofori, Richard Amfo-Otu, Isaac O. A. Hodgson

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The study was conducted to determine the treatment performance of waste stabilization ponds in Akosombo. A total of 15 samples were taken for four consecutive months from the inlet, facultative pond and outlet of maturation pond. The samples were preserved and transported to Water Research Institute for laboratory analysis. The wastewater quality parameters analysed to assess the treatment performance were total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia and phosphate. The results of the laboratory analysis showed that the ponds achieved TSS, BOD and COD removals of about 30, 82 and 75 per cent respectively. Statistically, the BOD (t = 10.27, p = 6.68 x 10-6) and COD (t = 4.23, p = 0.0029) of the raw sewage were significantly different from the total effluent at 95% confidence interval. The ammonia and phosphate removal was as high as 92% and 84% respectively. The quality parameters analysed for the final effluent from the Waste Stabilisation Pond was within the EPA guideline values. The general treatment performances were very good with respect to the parameters studied and does not pose threat to the receiving water body. A further study to examine the bacteriological treatment performance was recommended.

Keywords: waste stabilization pond, wast water, treatment performance, nutrient, Ghana

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Authors: Tomoaki Hashimoto

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Recently, feedback control systems using random dither quantizers have been proposed for linear discrete-time systems. However, the constraints imposed on state and control variables have not yet been taken into account for the design of feedback control systems with random dither quantization. Model predictive control is a kind of optimal feedback control in which control performance over a finite future is optimized with a performance index that has a moving initial and terminal time. An important advantage of model predictive control is its ability to handle constraints imposed on state and control variables. Based on the model predictive control approach, the objective of this paper is to present a control method that satisfies probabilistic state constraints for linear discrete-time feedback control systems with random dither quantization. In other words, this paper provides a method for solving the optimal control problems subject to probabilistic state constraints for linear discrete-time feedback control systems with random dither quantization.

Keywords: optimal control, stochastic systems, random dither, quantization

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Authors: Moustafa Ahmed, Ahmed Bakry, Fumio Koyama

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We report on the use of strong external optical feedback to enhance the modulation response of semiconductor lasers over a frequency passband around modulation frequencies higher than 60 GHz. We show that this modulation enhancement is a type of photon-photon resonance (PPR) of oscillating modes in the external cavity formed between the laser and the external reflector. The study is based on a time-delay rate equation model that takes into account both the strong feedback and multiple reflections in the external cavity. We examine the harmonic and intermodulation distortions associated with single and two-tone modulations in the mm-wave band of the resonant modulation. We show that compared with solitary lasers modulated around the carrier-photon resonance frequency, the present mm-wave modulated signal has lower distortions.

Keywords: semiconductor laser, optical feedback, modulation, harmonic distortion

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Authors: Ali Sinan Soğancı

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Expansive soils are often encountered in many parts of the world, especially in arid and semi-arid fields. Such kind of soils, generally including active clay minerals in low water content, enlarge in volume by absorbing the water through the surface and cause a great harm to the light structures such as channel coating, roads and airports. The expansive soils were encountered on the path of Apa-Hotamış conveyance channel belonging to the State Hydraulic Works in the region of Konya. In the research done in this area, it is predicted that the soil has a swollen nature and the soil should be filled with proper granular equipment by digging the ground to 50-60 cm. In this study, for purpose of helping the other research to be done in the same area, it is thought that instead of replacing swollen soil with the granular soil, by stabilizing it with polypropylene fiber and using it its original place decreases effect of swelling percent, in this way the cost will be decreased. Therefore, a laboratory tests were conducted to study the effects of polypropylene fiber on swelling characteristics of expansive soil. Test results indicated that inclusion of fiber reduced swell percent of expansive soil. As the fiber content increased, the unconfined compressive strength was increased. Finally, it can be say that stabilization of expansive soils with polypropylene fiber is an effective method.

Keywords: expansive soils, polypropylene fiber, stabilization, swelling percent

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Authors: Papitchaya Papangkorn

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Matching the expectations of teachers and learners is significant for successful language learning. Moreover, teachers should discover what their learners think and feel about what and how they want to learn. Therefore, this study investigates International College, Suan Sunandha Rajabhat University students’ preferences toward error corrections in order to help SSRUIC teachers match their expectations and their learners because it is important for successful language learning. This study examined the learners’ attitude and preference toward error correction through 50 first year SSRUIC students both male (25) and female (25) in Bangkok, Thailand. The data were collected from a questionnaire and interviews to investigate the necessity and frequency, timing, type of errors, method of corrective feedback, and person who gives error correction in order to answer the overall research question and sub-questions. The findings indicate five suggestions regarding the overall research question. Firstly, errors should be treated, and always be treated. Secondly, treating errors after finish speaking is the most appropriate time. Thirdly, “errors that may cause problems in an understanding of listener” and “frequent spoken errors” should be treated. Fourthly, repetition and explicit feedback were the most popular types of feedback among males, whereas metalinguistic feedback was the most favoured types amongst females. Finally, teachers were the most preferred person to deliver corrective feedback for the learners. Although the results of the study are difficult to generalize to a larger population, which are Thai EFL learners because of the small sample, the findings provide useful information that may contribute to understanding of SSRUIC learners’ preferences toward error corrections and it might reduce the gap between what teachers employ and what students expect when receiving corrective feedback. The reduction of this gap may be useful for the learning process and could enhance the efforts of both teachers and learners in a Thai context.

Keywords: attitude, corrective feedback, error, preference

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Authors: S. H. J. Liu

Abstract:

This paper aims to explore the role of peer Corrective Feedback (CF) in improving written productions by English-as-a- foreign-language (EFL) learners who work together via Wikispaces. It attempted to determine the effect of peer CF on form accuracy in English, such as grammar and lexis. Thirty-four EFL learners at the tertiary level were randomly assigned into the experimental (with peer feedback) or the control (without peer feedback) group; each group was subdivided into small groups of two or three. This resulted in six and seven small groups in the experimental and control groups, respectively. In the experimental group, each learner played a role as an assessor (providing feedback to others), as well as an assessee (receiving feedback from others). Each participant was asked to compose his/her written work and revise it based on the feedback. In the control group, on the other hand, learners neither provided nor received feedback but composed and revised their written work on their own. Data collected from learners’ compositions and post-task interviews were analyzed and reported in this study. Following the completeness of three writing tasks, 10 participants were selected and interviewed individually regarding their perception of collaborative learning in the Computer-Mediated Communication (CMC) environment. Language aspects to be analyzed included lexis (e.g., appropriate use of words), verb tenses (e.g., present and past simple), prepositions (e.g., in, on, and between), nouns, and articles (e.g., a/an). Feedback types consisted of CF, affective, suggestive, and didactic. Frequencies of feedback types and the accuracy of the language aspects were calculated. The results first suggested that accurate items were found more in the experimental group than in the control group. Such results entail that those who worked collaboratively outperformed those who worked non-collaboratively on the accuracy of linguistic aspects. Furthermore, the first type of CF (e.g., corrections directly related to linguistic errors) was found to be the most frequently employed type, whereas affective and didactic were the least used by the experimental group. The results further indicated that most participants perceived that peer CF was helpful in improving the language accuracy, and they demonstrated a favorable attitude toward working with others in the CMC environment. Moreover, some participants stated that when they provided feedback to their peers, they tended to pay attention to linguistic errors in their peers’ work but overlook their own errors (e.g., past simple tense) when writing. Finally, L2 or FL teachers or practitioners are encouraged to employ CMC technologies to train their students to give each other feedback in writing to improve the accuracy of the language and to motivate them to attend to the language system.

Keywords: peer corrective feedback, computer-mediated communication (CMC), second or foreign language (L2 or FL) learning, Wikispaces

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Authors: Ali Sinan Soğancı

Abstract:

Expansive soils are often encountered in many parts of the world, especially in arid and semi-arid fields. Such kind of soils, generally including active clay minerals in low water content, enlarge in volume by absorbing the water through the surface and cause a great harm to the light structures such as channel coating, roads and airports. The expansive soils were encountered on the path of Apa-Hotamış conveyance channel belonging to the State Hydraulic Works in the region of Konya. In the research done in this area, it is predicted that the soil has a swollen nature and the soil should be filled with proper granular equipment by digging the ground to 50-60 cm. In this study, for purpose of helping the other research to be done in the same area, it is thought that instead of replacing swollen soil with the granular soil, by stabilizing it with polypropylene fiber and using it its original place decreases effect of swelling percent, in this way the cost will be decreased. Therefore, a laboratory tests were conducted to study the effects of polypropylene fiber on swelling characteristics of expansive soil. Test results indicated that inclusion of fiber reduced swell percent of expansive soil. As the fiber content increased, the unconfined compressive strength was increased. Finally, it can be say that stabilization of expansive soils with polypropylene fiber is an effective method.

Keywords: expansive soils, polypropylene fiber, stabilization, swelling percent

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Authors: Orit Zeevy-Solovey

Abstract:

Grammar has traditionally been taught for its own sake, emphasizing rules and drills. However, in recent years, more emphasis is given to communicative competence. Current research suggests that form-focused instruction is notably efficient when incorporated in a meaningful communicative context. It is maintained that writing tasks related to the students’ academic fields will encourage them to express themselves openly in topics that are close to their hearts, without feeling too uneasy about grammatical forms. The teacher can further reduce students’ apprehension of grammar by announcing that credit will be given for merely doing the task and that grammar mistakes will not affect the grade. Students’ linguistic errors can then be corrected by giving metalinguistic feedback which involves providing learners with some kind of explicit remark about the nature of the errors they have made. Research has also shown that learners’ developmental readiness is an important factor influencing the effectiveness of written corrective feedback. Larger effect sizes appear as the proficiency level is higher. The purposes of this paper are to demonstrate how grammar can be taught indirectly through writing tasks, and more specifically, how the use of metalinguistic written corrective feedback given to advanced English as a Foreign Language (EFL) students can raise their linguistic awareness. Since errors are not directly corrected, the students have to work out the corrections needed through exploring grammar books and websites. Longitudinal studies of metalinguistic written corrective feedback comparing the number of errors in students’ first and fourth compositions have shown a decrease in errors.

Keywords: EFL, linguistic awareness, metalinguistic corrective feedback, teaching grammar through writing

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Authors: Millicent N. Khumalo, Phesheya E. Dlamini

Abstract:

Shrub-encroachment leads to a gain or loss of soil organic carbon (SOC) in previously open rangelands. The stabilization mechanisms controlling the storage of soil organic carbon (SOC) within aggregates of shrub-encroached grassland soils are poorly understood, especially in shallow plinthic soils. In this study, physical fractionation of surface soils (0- 10 cm) collected from open and shrub-encroached grasslands was conducted to determine the distribution of SOC within macro-and- microaggregates. Soil aggregates were classified into four fractions by a wet-sieving procedure, namely >2000 (large macro-aggregates), 212-2000 (small macro-aggregates), 50-212 (microaggregates) and < 50µm (silt+clay). In both shrub-encroached and open grassland soils, SOC was greater in the silt+clay fraction. In this fraction, SOC was on average 133% greater in shrub-encroached compared to open grassland. The greater SOC within the silt+clay fraction is due to the greater surface area and thus more exchange sites for carbon absorption. This implies that the SOC physically protected within the silt+clay is stored long-term.

Keywords: aggregate fractions, shrub-encroachment, soil organic carbon, stabilization

Procedia PDF Downloads 106