A study of the effect of harmonics in the system on the performance of residual current-operated circuit-breakers and electromechanical overcurrent relays

Residual current-operated circuit-breakers (RCCBs) have proved useful devices for the protection of both human beings against ventricular fibrillation and installations against fire. Although they work well with sinusoidal waveforms, there is little published information on their characteristics. Due to shunt connected non-linear devices, not the least of which is the use of power electronic equipment, the supply is distorted. Consequently, RCCBs as well as other protection relays are subject to non-sinusoidal current waveforms. Recent studies showed that RCCBs are greatly affected by harmonics, however the reasons for this are not clear. A literature search has also shown that there are inconsistencies in the analysis of the effect of harmonics on protection relays. In this work, the way RCCBs operate is examined, then a model is built with the aim of assessing the effect of non-sinusoidal current on RCCBs. Tests are then carried out on a number of RCCBs and these, when compared with the results from the model showed good correlation. In addition, the model also enables us to explain the RCCBs characteristics for pure sinusoidal current. In the model developed, various parameters are evaluated but special attention is paid to the instantaneous value of the current and the tripping mechanism movement. A similar assessment method is then used to assess the effect of harmonics on two types of protection relay, the electromechanical instantaneous relay and time overcurrent relay. A model is built for each of them which is then simulated on the computer. Tests results compare well with the simulation results, and thus the model developed can be used to explain the relays behaviour in a harmonics environment. The author's models, analysis and tests show that RCCBs and protection relays are affected by harmonics in a way determined by the waveform and the relay constants. The method developed provides a useful tool and the basic methodology to analyse the behaviour of RCCBs and protection relays in a harmonics environment. These results have many implications, especially the way RCCBs and relays should be tested if harmonics are taken into account.

Current practice and opinion in special schools for the maladjusted in England and Wales

This study seeks to describe current practice and opinion in schools for the maladjusted in England and Wales and to exarnlne how far this coincides with earlier descriptions. A review of the literature provides an account of this earlier work, and data accrued from questionnaires completed by 114 schools describe current practice and opinion. The study represents the most extensive empirical enquiry into the work of these schools since 1955 and provides a wide data basis for future research and assessment of progress and change. The data suggest that there is much communality of practice and opinion within the schools, with most schools emphasising their therapeutic rather than their educational purpose. The work is characterised by the wide use and perceived efficacy of warm, caring adult to child relationships, improvement of pupil self-image through success, and individual counselling and discussion, which permeate a structure of routine, discipline and educational concern. Specialised treatments are not used widely and involve only a minority of pupils. Practice tends to be in reference to conduct disordered pupils who are now perceived as the largest single disorder group within the schools, whereas previously neurotic disorders formed the largest single group. The majority of pupils are perceived as underachieving on entry and requiring remedial help: consequently the educational programme has a remedial bias. For staff, qualities of personality are considered to be more valuable than professional skills. The schools differ in the emphasis they allocate to one or more of four identified areas of treatment described as concern for pupils' needs; degree of pupil participation; theoretical orientation: and the use of external controls. There is a diminished reference to psychoanalytical theory and an increased reference to behaviourist theory relative to previous practice. Similarly, the use and perceived importance and effectiveness of pupil participation and unconditional affection has diminished.

Bromelain's activity and potential as an anti-cancer agent:Current evidence and perspectives

The medicinal qualities of pineapple are recognized in many traditions in South America, China and Southeast Asia. These qualities are attributed to bromelain, a 95%-mixture of proteases. Medicinal qualities of bromelain include anti-inflammatory, anti-thrombotic, fibrinolytic and anti-cancer functions. Existing evidence derived from clinical observations as well as from mouse- and cell-based models suggests that bromelain acts systemically, affecting multiple cellular and molecular targets. In recent years, studies have shown that bromelain has the capacity to modulate key pathways that support malignancy. It is now possible to suggest that the anti-cancer activity of bromelain consists in the direct impact on cancer cells and their micro-environment, as well as in the modulation of immune, inflammatory and haemostatic systems. This review will summarize existing data relevant to bromelain's anti-cancer activity and will suggest mechanisms which account for bromelain's effect, in the light of research involving non-cancer models. The review will also identify specific new research questions that will need to be addressed in order for a full assessment of bromelain-based anti-cancer therapy.

Guest editors’ introduction: is the HRM process important? Past, current, and future challenges

Ten years ago, Bowen and Ostroff (2004) criticized the one-sided focus on the content-based approach, where researchers take into account the inherent virtues (or vices) associated with the content of HR practices to explain performance. They explicitly highlight the role of the psychological processes through which employees attach meaning to HRM. In this first article of the special section entitled “Is the HRM Process Important?” we present an overview of past, current, and future challenges. For past challenges, we attempt to categorize the various research streams that originated from the seminal piece. To outline current challenges, we present the results of a content analysis of the original 15 articles put forward for the special section. In addition, we provide the overview of a caucus focused on this theme that was held at the Academy of Management annual meeting in Boston in 2012. In conclusion, we discuss future challenges relating to the HRM process approach and review the contributions that have been selected—against a competitive field—for this special issue