There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

This Review explains the concept of dissipative solitons and their application to high-energy mode-locked fibre laser cavities. Dynamics and effects such as dissipative soliton ‘explosions’ and ‘rain’ are summarized, and an outlook of the field is also provided.

/pdf/dissipative-solitons-for-mode-locked-lasers-1fudg0a89g.pdf

Dissipative solitons for mode-locked lasers

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

/pdf/step-up-dc-dc-converters-a-comprehensive-review-of-voltage-6dlytctzg2.pdf

Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

The Internet of Things (IoT) is the next era of communication. Using the IoT, physical objects can be empowered to create, receive, and exchange data in a seamless manner. Various IoT applications focus on automating different tasks and are trying to empower the inanimate physical objects to act without any human intervention. The existing and upcoming IoT applications are highly promising to increase the level of comfort, efficiency, and automation for the users. To be able to implement such a world in an ever-growing fashion requires high security, privacy, authentication, and recovery from attacks. In this regard, it is imperative to make the required changes in the architecture of the IoT applications for achieving end-to-end secure IoT environments. In this paper, a detailed review of the security-related challenges and sources of threat in the IoT applications is presented. After discussing the security issues, various emerging and existing technologies focused on achieving a high degree of trust in the IoT applications are discussed. Four different technologies, blockchain, fog computing, edge computing, and machine learning, to increase the level of security in IoT are discussed.

/pdf/a-survey-on-iot-security-application-areas-security-threats-1gb31j78px.pdf

A Survey on IoT Security: Application Areas, Security Threats, and Solution Architectures

We present extensive measurements of the pump-dependent dynamics of antiphase noise in a dual-wavelength multimode vertical-external-cavity surface-emitting laser (VECSEL). We show that antiphase noise at frequencies below 10 kHz dominates the relative-intensity noise spectrum in the emission of a dual-wavelength VECSEL due to gain competition between the two-lasing wavelengths. We observe that with increasing pump power the antiphase noise decreases in amplitude but increases in bandwidth. Surprisingly, at even higher pump powers the spectral extent of the antiphase noise narrows significantly. The results provide information critical to potential applications of dual-wavelength VECSELs, such as intracavity parametric frequency conversion.

Antiphase Noise Dynamics in a Dual-Wavelength Vertical-External-Cavity Surface-Emitting Laser

With a spike in popularity and sales, the electric vehicles (EVs) have revolutionized the transportation industry. As EV technology advances, the EVs are becoming more accessible and affordable. Therefore, a rapid proliferation of light-duty EVs have been noticed in the residential sector. Even though the increased charging demand of EVs is manageable in large-scale, the low-voltage (LV) residential networks might not be capable of managing localized capacity issues of large scale EV integration. Dynamic electricity tariff coupled with demand response and smart charging management can provide grid assistance to some extent. However, uncoordinated charging, if clustered in a residential distribution feeder, can risk grid assets because of overloading and can even jeopardize the reliability of the network by violating voltage constraints. This paper proposes a coordinated residential EV management system for power grid support. Charging and discharging of residential EV batteries are coordinated and optimized to address grid overloading during peak demand periods and voltage constraint violations. The EV management for grid support is formulated as a mixed-integer programming based optimization problem to minimize the inconveniences of EV owner while providing grid assistance. The proposed methodology is evaluated via a case study based on a residential feeder in Sydney, Australia with actual load demand data. The simulation results indicate the efficacy of the proposed EV management method for mitigating grid overloading and maintaining desired bus voltages.

A Multi-agent system based residential electric vehicle management system for grid-support service

The coupling in synchronous reference frame (dq-axis) of grid-connected inverter reduces the estimation accuracy of grid impedance based on variations of inverter's output power. Therefore, in this paper, an improved grid impedance estimation technique (at fundamental frequency) based on small variations of the inverter's output power is proposed. Moreover, to cope with unbalanced grid voltage conditions, the estimation algorithm is embedded in a positive-and negative-sequence controller (PNSC) strategy. The technique relies on obtaining three operating points produced from a deliberate variations in the dq-current references of the positive-sequence control loop. Adopting three operating points to estimate the grid impedance, significantly reduces the effects of the coupling in the dq-axis during variation of the output power without the need to set either the active or the reactive output power of the inverter to zero during the estimation. Hence, accurate estimation of grid impedance is obtained in a short period of time. Simulation results, using MATLAB\Simulink and PLECS toolbox based on a discrete-time model, show the reliability of the proposed grid impedance technique.

An Improved Grid Impedance Estimation Technique under Unbalanced Voltage Conditions

Pyrolysis is a well-established method of converting biomass to different types of value-added products, such as high energy density biofuels and chemicals. In this work, chicken-litter waste and r...

Energy Conversion Efficiency of Pyrolysis of Chicken Litter and Rice Husk Biomass

With the continuous increase in distributed energy resources that are being integrated into the utility grid, it becomes necessary for inverters to estimate the grid impedance online to be used for several applications. Despite the fact that online grid impedance estimation techniques using grid-connected inverters gained more attention recently, no comprehensive study has been evaluating the performance of different estimation techniques under several grid conditions. This study proposes an extensive comparison to assess the accuracy of two online frequency-based grid impedance estimation techniques at the fundamental frequency. These two techniques are based on the 75 Hz frequency injection technique and pseudo-random binary sequence injection, respectively. Results from MATLAB/Simulink and PLECS RT Box present the advantages and disadvantages of these estimation techniques and the required trade-offs. This comparison study analyses the effects of disturbance magnitude and its injection time, the variation of grid impedance and non-ideal grid voltage. Furthermore, solutions are proposed to enhance the estimation accuracy of both techniques for non-ideal grid voltage containing inter-harmonics and sub-harmonics. The study concludes with recommendations regarding the best use of these two frequency-based grid impedance estimation techniques to suit a particular low voltage grid scenario.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2019.1458

Graham Town

Papers

Antiphase Noise Dynamics in a Dual-Wavelength Vertical-External-Cavity Surface-Emitting Laser

A Multi-agent system based residential electric vehicle management system for grid-support service

An Improved Grid Impedance Estimation Technique under Unbalanced Voltage Conditions

Energy Conversion Efficiency of Pyrolysis of Chicken Litter and Rice Husk Biomass

Fundamental grid impedance estimation using grid-connected inverters: a comparison of two frequency-based estimation techniques