Intensity dynamics and statistical properties of random distributed feedback fiber laser

We present first experimental investigation of fast-intensity dynamics of random distributed feedback (DFB) fiber lasers. We found that the laser dynamics are stochastic on a short time scale and exhibit pronounced fluctuations including generation of extreme events. We also experimentally characterize statistical properties of radiation of random DFB fiber lasers. We found that statistical properties deviate from Gaussian and depend on the pump power.

Random distributed feedback fiber laser

I will overview our recent results on ultra-long lasers and will discuss the concept of a fiber laser with an open cavity that operates using random distributed feedback provided by Rayleigh scattering amplified through the Raman effect. © 2011 Optical Society of America.

Supporting learners’ agentic engagement with feedback:a systematic review and a taxonomy of recipience processes

Much has been written in the educational psychology literature about effective feedback and how to deliver it. However, it is equally important to understand how learners actively receive, engage with, and implement feedback. This article reports a systematic review of the research evidence pertaining to this issue. Through an analysis of 195 outputs published between 1985 and early 2014, we identified various factors that have been proposed to influence the likelihood of feedback being used. Furthermore, we identified diverse interventions with the common aim of supporting and promoting learners' agentic engagement with feedback processes. We outline the various components used in these interventions, and the reports of their successes and limitations. Moreover we propose a novel taxonomy of four recipience processes targeted by these interventions. This review and taxonomy provide a theoretical basis for conceptualizing learners' responsibility within feedback dialogues and for guiding the strategic design and evaluation of interventions. Receiving feedback on one's skills and understanding is an invaluable part of the learning process, benefiting learners far more than does simply receiving praise or punishment (Black & Wiliam, 1998 Black, P., & Wiliam, D. (1998). Assessment and classroom learning. Assessment in Education: Principles, Policy & Practice, 5, 7–74. doi:10.1080/0969595980050102[Taylor & Francis Online]; Hattie & Timperley, 2007 Hattie, J., & Timperley, H. (2007). The power of feedback. Review of Educational Research, 77, 81–112. doi:10.3102/003465430298487[CrossRef], [Web of Science ®]). Inevitably, the benefits of receiving feedback are not uniform across all circumstances, and so it is imperative to understand how these gains can be maximized. There is increasing consensus that a critical determinant of feedback effectiveness is the quality of learners' engagement with, and use of, the feedback they receive. However, studies investigating this engagement are underrepresented in academic research (Bounds et al., 2013 Bounds, R., Bush, C., Aghera, A., Rodriguez, N., Stansfield, R. B., & Santeen, S. A. (2013). Emergency medicine residents' self-assessments play a critical role when receiving feedback. Academic Emergency Medicine, 20, 1055–1061. doi:10.1111/acem.12231[CrossRef], [PubMed], [Web of Science ®]), which leaves a “blind spot” in our understanding (Burke, 2009 Burke, D. (2009). Strategies for using feedback students bring to higher education. Assessment & Evaluation in Higher Education, 34, 41–50. doi:10.1080/02602930801895711[Taylor & Francis Online], [Web of Science ®]). With this blind spot in mind, the present work sets out to systematically map the research literature concerning learners' proactive recipience of feedback. We use the term “proactive recipience” here to connote a state or activity of engaging actively with feedback processes, thus emphasizing the fundamental contribution and responsibility of the learner (Winstone, Nash, Rowntree, & Parker, in press Winstone, N. E., Nash, R. A., Rowntree, J., & Parker, M. (in press). ‘It'd be useful, but I wouldn't use it’: Barriers to university students' feedback seeking and recipience. Studies in Higher Education. doi: 10.1080/03075079.2015.1130032[Taylor & Francis Online]). In other words, just as Reeve and Tseng (2011 Reeve, J., & Tseng, M. (2011). Agency as a fourth aspect of student engagement during learning activities. Contemporary Educational Psychology, 36, 257–267. doi:10.1016/j.cedpsych.2011.05.002[CrossRef], [Web of Science ®]) defined “agentic engagement” as a “student's constructive contribution into the flow of the instruction they receive” (p. 258), likewise proactive recipience is a form of agentic engagement that involves the learner sharing responsibility for making feedback processes effective.

Negative feedback regulation of the ERK1/2 MAPK pathway

The extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) signalling pathway regulates many cellular functions, including proliferation, differentiation, and transformation. To reliably convert external stimuli into specific cellular responses and to adapt to environmental circumstances, the pathway must be integrated into the overall signalling activity of the cell. Multiple mechanisms have evolved to perform this role. In this review, we will focus on negative feedback mechanisms and examine how they shape ERK1/2 MAPK signalling. We will first discuss the extensive number of negative feedback loops targeting the different components of the ERK1/2 MAPK cascade, specifically the direct posttranslational modification of pathway components by downstream protein kinases and the induction of de novo gene synthesis of specific pathway inhibitors. We will then evaluate how negative feedback modulates the spatiotemporal signalling dynamics of the ERK1/2 pathway regarding signalling amplitude and duration as well as subcellular localisation. Aberrant ERK1/2 activation results in deregulated proliferation and malignant transformation in model systems and is commonly observed in human tumours. Inhibition of the ERK1/2 pathway thus represents an attractive target for the treatment of malignant tumours with increased ERK1/2 activity. We will, therefore, discuss the effect of ERK1/2 MAPK feedback regulation on cancer treatment and how it contributes to reduced clinical efficacy of therapeutic agents and the development of drug resistance.

The construction and negotiation of identity and face in post observation feedback

Identity influences the practice of English language teachers and supervisors, their professional development and their ability to incorporate innovation and change. Talk during post observation feedback meetings provides participants with opportunities to articulate, construct, verify, contest and negotiate identities, processes which often engender issues of face. This study examines the construction and negotiation of identity and face in post observation feedback meetings between in-service English language teachers and supervisors at a tertiary institution in the United Arab Emirates. Within a linguistic ethnography framework, this study combined linguistic microanalysis of audio recorded feedback meetings with ethnographic data gathered from participant researcher knowledge, pre-analysis interviews and post-analysis participant interpretation interviews. Through a detailed, empirical description of situated ‘real life’ institutional talk, this study shows that supervisors construct identities involving authority, power, expertise, knowledge and experience while teachers index identities involving experience, knowledge and reflection. As well as these positive valued identities, other negative, disvalued identities are constructed. Identities are shown to be discursively claimed, verified, contested and negotiated through linguistic actions. This study also shows a link between identity and face. Analysis demonstrates that identity claims verified by an interactional partner can lead to face maintenance or support. However, a contested identity claim can lead to face threat which is usually managed by facework. Face, like identity, is found to be interactionally achieved and endogenous to situated discourse. Teachers and supervisors frequently risk face threat to protect their own identities, to contest their interactional partner’s identities or to achieve the feedback meeting goal i.e. improved teaching. Both identity and face are found to be consequential to feedback talk and therefore influence teacher development, teacher/supervisor relationships and the acceptance of feedback. Analysis highlights the evaluative and conforming nature of feedback in this context which may be hindering opportunities for teacher development.

Random distributed feedback fiber laser

Researchers conducted investigations to demonstrate the advantages of random distributed feedback fiber laser. Random lasers had advantages, such as simple technology that did not require a precise microcavity and low production cost. The properties of their output radiation were special in comparison to those of conventional lasers and they were characterized by complex features in the spatial, spectral, and time domains. The researchers demonstrated a new type of one-dimensional laser with random distributed feedback based on Rayleigh scattering (RS) that was presented in any transparent glass medium due to natural inhomogeneities of refractive index. The cylindrical fiber waveguide geometry provided transverse confinement, while the cavity was open in the longitudinal direction and did not include any regular point-action reflectors.

Raman fiber lasers with a random distributed feedback based on Rayleigh scattering

We demonstrate lasing based on a random distributed feedback due to the Raman amplified Rayleigh backscattering in different types of cavities with and without conventional point-action reflectors. Quasistationary generation of a narrowband spectrum is achieved despite the random nature of the feedback. The generated spectrum is localized at the reflection or gain spectral maxima in schemes with and without point reflectors, respectively. The length limit for a conventional cavity and the minimal pump power required for the lasing based purely on a random distributed feedback are determined. © 2010 The American Physical Society.