45 research outputs found
An experience with teaching squares
Teaching Squares is a technique which was developed in 2001, is now used at numerous
universities worldwide, and is aimed at informing and improving teaching [1]. It uses a process of
classroom observation combined with personal and group reflection, while being free from the pressure of
peer observations typically performed for the purpose of evaluation. For the initial trial of this technique
at Nazarbayev University, three groups of four professors each (3 squares) were selected from across the
university. We report the experience of our square
PT-Symmetric Talbot Effects
We show that complex PT-symmetric photonic lattices can lead to a new class
of self-imaging Talbot effects. For this to occur, we find that the input field
pattern, has to respect specific periodicities which are dictated by the
symmetries of the system. While at the spontaneous PT-symmetry breaking point,
the image revivals occur at Talbot lengths governed by the characteristics of
the passive lattice, at the exact phase it depends on the gain and loss
parameter thus allowing one to control the imaging process.Comment: 5 pages, 3 figure
Bragg solitons in nonlinear PT-symmetric periodic potentials
It is shown that slow Bragg soliton solutions are possible in nonlinear
complex parity-time (PT) symmetric periodic structures. Analysis indicates that
the PT-symmetric component of the periodic optical refractive index can modify
the grating band structure and hence the effective coupling between the forward
and backward waves. Starting from a classical modified massive Thirring model,
solitary wave solutions are obtained in closed form. The basic properties of
these slow solitary waves and their dependence on their respective PT-symmetric
gain/loss profile are then explored via numerical simulations.Comment: 6 pages, 4 figures, published in Physical Review
Coexisting periodic attractors in injection locked diode lasers
We present experimental evidence for coexisting periodic attractors in a
semiconductor laser subject to external optical injection. The coexisting
attractors appear after the semiconductor laser has undergone a Hopf
bifurcation from the locked steady state. We consider the single mode rate
equations and derive a third order differential equation for the phase of the
laser field. We then analyze the bifurcation diagram of the time periodic
states in terms of the frequency detuning and the injection rate and show the
existence of multiple periodic attractors.Comment: LaTex, 14 pages, 6 postscript figures include
Stability of the nonlinear dynamics of an optically injected VCSEL
Automated protocols have been developed to characterize time series data in terms of stability. These techniques are applied to the output power time series of an optically injected vertical cavity surface emitting laser (VCSEL) subject to varying injection strength and optical frequency detuning between master and slave lasers. Dynamic maps, generated from high resolution, computer controlled experiments, identify regions of dynamic instability in the parameter space. © 2012 Optical Society of America
Performance characteristics of positive and negative delayed feedback on chaotic dynamics of directly modulated InGaAsP semiconductor lasers
The chaotic dynamics of directly modulated semiconductor lasers with delayed
optoelectronic feedback is studied numerically. The effects of positive and
negative delayed optoelectronic feedback in producing chaotic outputs from such
lasers with nonlinear gain reduction in its optimum value range is investigated
using bifurcation diagrams. The results are confirmed by calculating the
Lyapunov exponents. A negative delayed optoelectronic feedback configuration is
found to be more effective in inducing chaotic dynamics to such systems with
nonlinear gain reduction factor in the practical value range.Comment: 18 pages, 16 figures. To appear In Pramana - journal of physic
A multi-disciplinary perspective on emergent and future innovations in peer review [version 2; referees: 2 approved]
Peer review of research articles is a core part of our scholarly communication system. In spite of its importance, the status and purpose of peer review is often contested. What is its role in our modern digital research and communications infrastructure? Does it perform to the high standards with which it is generally regarded? Studies of peer review have shown that it is prone to bias and abuse in numerous dimensions, frequently unreliable, and can fail to detect even fraudulent research. With the advent of web technologies, we are now witnessing a phase of innovation and experimentation in our approaches to peer review. These developments prompted us to examine emerging models of peer review from a range of disciplines and venues, and to ask how they might address some of the issues with our current systems of peer review. We examine the functionality of a range of social Web platforms, and compare these with the traits underlying a viable peer review system: quality control, quantified performance metrics as engagement incentives, and certification and reputation. Ideally, any new systems will demonstrate that they out-perform and reduce the biases of existing models as much as possible. We conclude that there is considerable scope for new peer review initiatives to be developed, each with their own potential issues and advantages. We also propose a novel hybrid platform model that could, at least partially, resolve many of the socio-technical issues associated with peer review, and potentially disrupt the entire scholarly communication system. Success for any such development relies on reaching a critical threshold of research community engagement with both the process and the platform, and therefore cannot be achieved without a significant change of incentives in research environments
Factors influencing the scientific performance of Momentum grant holders: an evaluation of the first 117 research groups
A multi-disciplinary perspective on emergent and future innovations in peer review
Peer review of research articles is a core part of our scholarly communication system. In spite of its importance, the status and purpose of peer review is often contested. What is its role in our modern digital research and communications infrastructure? Does it perform to the high standards with which it is generally regarded? Studies of peer review have shown that it is prone to bias and abuse in numerous dimensions, frequently unreliable, and can fail to detect even fraudulent research. With the advent of web technologies, we are now witnessing a phase of innovation and experimentation in our approaches to peer review. These developments prompted us to examine emerging models of peer review from a range of disciplines and venues, and to ask how they might address some of the issues with our current systems of peer review. We examine the functionality of a range of social Web platforms, and compare these with the traits underlying a viable peer review system: quality control, quantified performance metrics as engagement incentives, and certification and reputation. Ideally, any new systems will demonstrate that they out-perform and reduce the biases of existing models as much as possible. We conclude that there is considerable scope for new peer review initiatives to be developed, each with their own potential issues and advantages. We also propose a novel hybrid platform model that could, at least partially, resolve many of the socio-technical issues associated with peer review, and potentially disrupt the entire scholarly communication system. Success for any such development relies on reaching a critical threshold of research community engagement with both the process and the platform, and therefore cannot be achieved without a significant change of incentives in research environments