Search results for "Feedback"
showing 10 items of 538 documents
Dynamic Output Feedback Passive Control of Uncertain Switched Stochastic Systems with Time-Varying Delay
2013
Published version of an article in the journal: Mathematical Problems in Engineering. Also available from Hindawi: http://dx.doi.org/10.1155/2013/281747 Open Access This paper is concerned with the issues of passivity analysis and dynamic output feedback (DOF) passive control for uncertain switched stochastic systems with time-varying delay via multiple storage functions (MSFs) method. Firstly, based on the MSFs method, a sufficient condition for the existence of the passivity of the underlying system is established in terms of linear matrix inequalities (LMIs). Furthermore, the problem of dynamic output feedback passive control is investigated. Based on the obtained passivity condition, a …
Fiber laser switched by a long period grating interferometer as an intra-cavity loss modulator
2010
Abstract In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz.
Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating.
2009
We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.
Fiber laser with combined feedback of core and cladding modes assisted by an intracavity long-period grating
2011
We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.
Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating
2009
We report an actively Q-switched all-fiber laser based on magnetostriction modulation of a Bragg grating. The laser employs a pair of Bragg gratings as reflective mirrors, one of which is bonded to a magnetostrictive element. Lengthening of the magnetostrictive element when a magnetic field is applied shifts the Bragg wavelength of the grating, allowing control of the Q-factor of the cavity and, thus, performing active Q-switching. The magnetostrictive modulator is small, compact and requires less than 300 mW electrical drive power. Using erbium-doped fiber and a maximum pump power of 120 mW, Q-switch pulses of more than 1 W peak power were obtained, with a pulse repetition rate that can be…
High-Resolution Nonlinear Raman-Spectroscopy in Gases
1990
0377-0486; The resolution in the Raman spectra of gases has been greatly improved by the development of the different methods of non-linear Raman scattering. When two laser beams, one of which has a tunable frequency, are focused in a sample, a stimulated Raman process occurs as soon as the frequency difference between the two lasers is equal to a Raman-active rovibrational or rotational transition frequency. The Raman resonance can be detected in different ways: by coherent anti-Stokes Raman scattering (CARS) or the corresponding Stokes process (CSRS), by a gain in one of the beams (stimulated Raman gain spectroscopy, SRGS) or a loss in the other (inverse Raman spectroscopy, IRS), or even …
Comparison of the effect of pharmacotherapy and neuro-feedback therapy on oral health of children with attention deficit hyperactivity disorder
2018
Background Attention deficit hyperactivity disorder (ADHD) is a chronic and progressive mental disorder related to the childhood period. This study aims to compare the oral health of two groups of ADHD children: those under pharmacotherapy and those under neuro-feedback therapy. Material and methods 72 ADHD children (aged 6-12) were divided into two 36 member groups: The pharmacotherapy group and the neuro-feedback therapy group. Unstimulated salivary flow (USF), DMFT, and plaque index were assessed in these children. Statistical analysis was carried out on the data with the independent t-test, which was performed using SPSS 16. The significance level of the study was p Results In this stud…
Peer assessment based assignment to enhance interactions in online learning groups
2015
In this paper, we report on the findings from our PhD work on how peer assessment based assignment method can enhance interaction in online learning groups. The method is explored and tried out on the research methods course on the Bachelor of Commerce Programme which is run in distance learning mode at Makerere University. Based on the idea that learning groups can enhance effective learning in online learning environments, we used the affordance eLearning framework to design the peer assessment based assignment task and then qualitative methods collect and report on data. The results reveal that there was increased interaction through peer feedback. Students were motivated because of the …
Adaptive formative feedback to improve strategic search decisions in task-oriented reading
2014
This study analyses the effectiveness of adaptive formative feedback to boost strategic search decisions and performance when students are asked to answer a set of questions in a task-oriented reading situation. We compared automatic feedback that included information about the right answer with feedback that also included the connection between the students' strategic search decisions and their performance. Ninety-two high school students read two non-continuous texts. They received feedback during a training phase, and then they read and also received feedback with a similar text in a final phase. Text and questions were presented using a new computer-based technology that provided automa…
Motivating Low-Achievers—Relative Performance Feedback in Primary Schools
2021
Abstract Relative performance feedback (RPF) has often been shown to improve effort and performance in the workplace and educational settings. Yet, many studies also document substantial negative effects of RPF, in particular for low-achievers. We study a novel type of RPF designed to overcome these negative effects of RPF on low-achievers by scoring individual performance improvements. With a sample of 400 children, we conduct a class-wise randomized-controlled trial using an e-learning software in regular teaching lessons in primary schools. We demonstrate that this type of RPF significantly increases motivation, effort, and performance in math for low-achieving children, without hurting …