Purpose built teaching equipment for a laboratory based course in three phase machines and drives

The hazards associated with high voltage three phase inverters and the rotating shafts of large electrical machines have resulted in most of the engineering courses covering these topics to be predominantly theoretical. This paper describes a set of purpose built, low voltage and low cost teaching equipment which allows the "hands on" instruction of three phase inverters and rotating machines. By using low voltages, the student can experiment freely with the motors and inverter and can access all of the current and voltage waveforms, which until now could only be studied in text books or observed as part of laboratory demonstrations. Both the motor and the inverter designs are optimized for teaching purposes cost around $25 and can be made with minimal effort.

Three-phase machines and drives - equipment for a laboratory-based course

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost

Wind turbine blade pitch control system

The present invention provides an improvement for a wind turbine (20) having at least one blade (21) mounted on a hub (22) for controlled rotation about a blade axis (yb-yb) to vary the pitch of the blade relative to an airstream. The hub is mounted on a nacelle (23) for rotation about a hub axis (xh-xh). The wind turbine includes a main pitch control system for selectively controlling the pitch of the blade, and/or a safety pitch control system for overriding the main blade pitch control system and for causing the blade to move toward a feathered position in the event of an overspeed or fault condition. The improvement includes: an energy storage device (26) mounted on the nacelle and associated with the blade; a pitch-axis controller (25) mounted on the nacelle and associated with the blade and with the energy storage device; an electro-mechanical actuator (28) mounted on the hub and associated with the blade; and at least one slip ring (29) operatively arranged to transmit power and/or data signals between the pitch-axis controller and the electro-mechanical actuator; whereby the mass on the rotating hub may be reduced.

An overview of Earth’s global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.

Vibrational perturbation theory

Expressions are derived for the Jacobian of the coriolis ζ interaction constants and the centrifugal stretching constants (DJ, DJK, etc.) with respect to the force constants in a vibrating-rotating molecule.

Analysis of the eyes formed in simulated tropical cyclones and polar lows

The structure and size of the eyes generated in numerically simulated tropical cyclones and polar lows have been studied. A primitive-equation numerical model simulated systems in which the structures of the eyes formed were consistent with available observations. Whilst the tropical cyclone eyes generated were usually rapidly rotating, it appeared impossible for an eye formed in a system with a polar environment to develop this type of structure. The polar low eyes were found to be unable to warm through the subsidence of air with high values of potential temperature, as the environment was approximately statically neutral. Factors affecting the size of the eye were investigated through a series of controlled experiments. In mature tropical cyclone systems the size of the eye was insensitive to small changes in initial conditions, surface friction and latent and sensible heating from the ocean. In contrast, the eye size was strongly dependent on these parameters in the mature polar lows. Consistent with the findings, a mechanism is proposed in which the size of the eye in simulated polar lows is controlled by the strength of subsidence within it.

Numerical simulation of the 12 May 1997 CME Event: The role of magnetic reconnection

We perform a numerical study of the evolution of a Coronal Mass Ejection (CME) and its interaction with the coronal magnetic field based on the 12 May 1997, CME event using a global MagnetoHydroDynamic (MHD) model for the solar corona. The ambient solar wind steady-state solution is driven by photospheric magnetic field data, while the solar eruption is obtained by superimposing an unstable flux rope onto the steady-state solution. During the initial stage of CME expansion, the core flux rope reconnects with the neighboring field, which facilitates lateral expansion of the CME footprint in the low corona. The flux rope field also reconnects with the oppositely orientated overlying magnetic field in the manner of the breakout model. During this stage of the eruption, the simulated CME rotates counter-clockwise to achieve an orientation that is in agreement with the interplanetary flux rope observed at 1 AU. A significant component of the CME that expands into interplanetary space comprises one of the side lobes created mainly as a result of reconnection with the overlying field. Within 3 hours, reconnection effectively modifies the CME connectivity from the initial condition where both footpoints are rooted in the active region to a situation where one footpoint is displaced into the quiet Sun, at a significant distance (≈1R ) from the original source region. The expansion and rotation due to interaction with the overlying magnetic field stops when the CME reaches the outer edge of the helmet streamer belt, where the field is organized on a global scale. The simulation thus offers a new view of the role reconnection plays in rotating a CME flux rope and transporting its footpoints while preserving its core structure.

The role of exotic plants in the invasion of Seychelles by the polyphagous insect Aleurodicus disperses: a phylogenetically controlled analysis

The accidental introduction of the spiralling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae) to Seychelles in late 2003 is exploited during early 2005 to study interactions between A. dispersus, native and exotic host plants and their associated arthropod fauna. The numbers of A. dispersus egg spirals and pupae, predator and herbivore taxa were recorded for eight related native/exotic pairs of host plants found on Mahe, the largest island in Seychelles. Our data revealed no significant difference in herbivore density (excluding A. dispersus) between related native and exotic plants, which suggests that the exotic plants do not benefit from 'enemy release'. There were also no differences in predator density, or combined species richness between native and exotic plants. Together these data suggest that 'biotic resistance' to invasion is also unlikely. Despite the apparent lack of differences in community structure significantly fewer A. dispersus egg spirals and pupae were found on the native plants than on the exotic plants. Additional data on A. dispersus density were collected on Cousin Island, a managed nature reserve in which exotic plants are carefully controlled. Significantly higher densities of A. dispersus were observed on Mahe, where exotic plants are abundant, than on Cousin. These data suggest that the rapid invasion of Seychelles by A. dispersus may largely be due to the high proportion of plant species that are both exotic and hosts of A. dispersus; no support was found for either the 'enemy release' or the 'biotic resistance' hypotheses.

Electrochemical and sonoelectrochemical monitoring of indigo reduction by glucose

The reduction of indigo (dispersed in water) to leuco-indigo (dissolved in water) is an important industrial process and investigated here for the case of glucose as an environmentally benign reducing agent. In order to quantitatively follow the formation of leuco-indigo two approaches based on (i) rotating disk voltammetry and (ii) sonovoltammetry are developed. Leuco-indigo, once formed in alkaline solution, is readily monitored at a glassy carbon electrode in the mass transport limit employing hydrodynamic voltammetry. The presence of power ultrasound further improves the leuco-indigo determination due to additional agitation and homogenization effects. While inactive at room temperature, glucose readily reduces indigo in alkaline media at 65 degrees C. In the presence of excess glucose, a surface dissolution kinetics limited process is proposed following the rate law d eta(leuco-indigo)/dt = k x c(OH-) x S-indigo where eta(leuco-indigo) is the amount of leuco-indigo formed, k = 4.1 x 10(-9) m s(-1) (at 65 degrees C, assuming spherical particles of I gm diameter) is the heterogeneous dissolution rate constant,c(OH-) is the concentration of hydroxide, and Sindigo is the reactive surface area. The activation energy for this process in aqueous 0.2 M NaOH is E-A = 64 U mol(-1) consistent with a considerable temperature effects. The redox mediator 1,8-dihydroxyanthraquinone is shown to significantly enhance the reaction rate by catalysing the electron transfer between glucose and solid indigo particles. (c) 2006 Elsevier Ltd. All fights reserved.

The genus Borassus (Arecaceae) in West Africa, with a description of a new species from Burkina Faso

Borassus akeassii Bayton, Ouedraogo & Guinko sp. nov. (Arecaceae) is described as a new species from western Burkina Faso in West Africa. It has been confused with the widely distributed African species B. aethiopum and more recently with the Asian B. flabellifer. However, it is distinguished by its glaucous, green leaves with weakly armed petioles and a characteristic pattern of lamina venation. The fruits have a pointed apex and are greenish when ripe, and the flowers of the pistillate inflorescence are arranged in three spirals. The pollen has a reticulate tectum and distinctive ornamentation. The distribution of B. akeassii is discussed and the status of the varieties of Borassus aethiopum (var. bagamojensis and var. senegalensis) is examined. (c) 2006 The Linnean Society of London.

Slicing of soft, flexible solids with industrial applications

Thin slices of soft flexible solids have negligible bending resistance and hence store negligible elastic strain energy; furthermore such offcuts are rarely permanently deformed after slicing. Cutting forces thus depend only on work of separation (toughness work) and friction. These simplifying assumptions are not as restrictive as it might seem, and the mechanics are found to apply to a wide variety of foodstuffs and biological materials. The fracture toughness of such materials may be determined from cutting experiments: the use of scissors instrumented for load and displacement is a popular method where toughness is obtained from the work areas beneath load–displacement plots. Surprisingly, there is no analysis for the variation of forces with scissor blade opening and this paper provides the theory. Comparison is made with experimental results in cutting with scissors. The analysis is generalised to cutting with blades of variable curvature and applied to a commercial food cutting device having a rotating spiral plan form blade. The strong influence of the ‘slice/push ratio’ (blade tangential speed to blade edge normal speed) on the cutting forces is revealed. Small cutting forces are important in food cutting machinery as damage to slices is minimised. How high slice/push ratios may be achieved by choice of blade profile is discussed.

Purpose built teaching equipment for a laboratory based course in three phase machines and drives

The hazards associated with high voltage three phase inverters ond the rotating sha@s of large electrical machines have resulted in most of the engineering courses covering these topics to be predominantly theoretical. This paper describes a set of purpose built, low voltage and low cost teaching equipment which allows the “hands on I’ instruction of three phase inverters and rotating machines. By using low voltages, the student can experiment freely with the motors and inverter and can access all of the current and voltage waveforms, which until now could only be studied in text books or observed as part of laboratory demonstrations. Both the motor and the inverter designs are optimized for teaching purposes, cost around $25 and can be made with minimal effort.

Three-phase machines and drives - Equipment for a laboratory-based course

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost.

The role of visual and nonvisual information in the control of locomotion

During locomotion, retinal flow, gaze angle, and vestibular information can contribute to one's perception of self-motion. Their respective roles were investigated during active steering: Retinal flow and gaze angle were biased by altering the visual information during computer-simulated locomotion, and vestibular information was controlled through use of a motorized chair that rotated the participant around his or her vertical axis. Chair rotation was made appropriate for the steering response of the participant or made inappropriate by rotating a proportion of the veridical amount. Large steering errors resulted from selective manipulation of retinal flow and gaze angle, and the pattern of errors provided strong evidence for an additive model of combination. Vestibular information had little or no effect on steering performance, suggesting that vestibular signals are not integrated with visual information for the control of steering at these speeds.

Mental rotation in Williams syndrome: an impaired ability

Typically developing young children and individuals with intellectual disabilities often perform poorly on mental rotation tasks when the stimulus they are rotating lacks a salient component. However. performance can he improved when salience is increased. The present study investigated the effect of salience oil mental rotation performance by individuals with Williams syndrome. Individuals with Williams syndrome and matched controls were presented with two versions of a mental rotation task: a no salient component condition and a salient component condition. The results showed that component salience did not benefit individuals with Williams syndrome in the same manner as it did controls.