Sensored and sensorless speed control methods for brushless doubly fed reluctance motors

The study considers aspects of scalar V/f control, vector control and direct torque (and flux) control (DTC) of the brushless doubly fed reluctance machine (BDFRM) as a promising cost-effective alternative to the existing technological solutions for applications with restricted variable speed capability such as large pumps and wind turbine generators. Apart from providing a comprehensive literature review and analysis of these control methods, the development and results of experimental verification, of an angular velocity observerbased DTC scheme for sensorless speed control of the BDFRM which, unlike most of the other DTC-concept applications, can perform well down to zero supply frequency of the inverter-fed winding, have also been presented in the study

A physical model of quantum cascade lasers: Application to GaAs, GaN and SiGe devices

The philosophy behind this work has been to build a predictive bottom up physical model of quantum cascade lasers (QCLs) for use as a design tool, to interpret experimental results and hence improve understanding of the physical processes occurring inside working devices and as a simulator for developing new material systems. The standard model uses the envelope function and effective mass approximations to solve two complete periods of the QCL under an applied bias. Other models, such as k·p and empirical pseudopotential, have been employed in p-type systems where the more complex band structure requires it. The resulting wave functions are then used to evaluate all relevant carrier-phonon, carrier-carrier and alloy scattering rates from each quantised state to all others within the same and the neighbouring period. This information is then used to construct a rate equation for the equilibrium carrier density in each subband and this set of coupled rate equations are solved self-consistently to obtain the carrier density in each eigenstate. The latter is a fundamental description of the device and can be used to calculate the current density and gain as a function of the applied bias and temperature, which in turn yields the threshold current and expected temperature dependence of the device characteristics. A recent extension which includes a further iteration of an energy balance equation also yields the average electron (or hole) temperature over the subbands. This paper will review the method and describe its application to mid-infrared and terahertz, GaAs, GaN, SiGe cascade laser designs

Thermal effects in InGaAs/AlAsSb quantum-cascade lasers

A quantum-cascade laser (QCL) thermal model is presented. On the basis of a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active-region temperature, which has a major influence on the device performance. A buried heterostructure combined with epilayer-down mounting is found to offer the best performance compared with alternative structures and has thermal time constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures

Bacillus spp. as potential biocontrol agents of bacterial spot on pepper caused by xanthomonas euvesicatoria

The objective of this research was to identify bacterial spot-causing pathogen and bacterial antagonists for management of the disease using biocontrol agents as environmentally friendly alternatives. Isolates of Bacillus spp. were obtained from the soil samples collected at different localities in Serbia. Antibacterial activity of natural antagonists toward the pathogen isolated from infected pepper leaves was examined using a modified well-diffusion assay and standard germination test. Our results confirmed the presence of Xanthomonas euvesicatoria as the causal agent of bacterial spot of pepper. Screening of 32 Bacillus spp. isolates for antibacterial activity showed that 8 isolates inhibit growth of examined X. euvesicatoria isolates. Four isolates identified as Bacillus subtilis exhibited the highest antibacterial activity by in vitro test (from 5 to 14 mm inhibition zone of bacterial growth). The isolates positively influenced germination of pepper seeds, causing up to 16% and 70% increase in germination and germination viability compared to control seeds infected with pathogen. The most effective isolates of Bacillus subtilis could be used as potential biocontrol agents of bacterial spot of pepper

X-ray Nanodiffraction on a Single SiGe Quantum Dot inside a Functioning Field-Effect Transistor

For advanced electronic, optoelectronic, or mechanical nanoscale devices a detailed understanding of their structural properties and in particular the strain state within their active region is of utmost importance. We demonstrate that X-ray nanodiffraction represents an excellent tool to investigate the internal structure of such devices in a nondestructive way by using a focused synchotron X-ray beam with a diameter of 400 nm. We show results on the strain fields in and around a single SiGe island, which serves as stressor for the Si-channel in a fully functioning Si-metal-oxide semiconductor field-effect transistor

Sparsity-promoting optimal control for a class of distributed systems

Abstract — We consider a linear quadratic optimal control problem with an additional penalty on the number of commu-nication links in the distributed controller. We reformulate this combinatorial optimization problem as a sequence of weighted `1 problems, where the weighted `1 norm approximates the counting of the communication links. We identify a class of systems for which the weighted `1 problem can be formulated as a semidefinite program and therefore its solution can be com-puted efficiently. Application of the developed algorithm to the optimal control of vehicular formations reveals communication topologies that become sparser as the price of inter-vehicular communications is increased. Index Terms — Communication architecture, convex opti-mization, `1 minimization, reweighting, semidefinite program

Cost-efficiency benchmarking of European air navigation service providers

This study uses EUROCONTROL data on operating performance of the national air navigation service providers over the 2002-2011 time period to document in detail the efficiency changes across providers and time using data envelopment analysis. Our results suggest that overall providers' productivity improved over the time period covered by the data, driven by improvements in technical rather than allocative efficiency. However, some trend reversals in the post-2008 crisis period are also observed