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The impact ionization characteristics of (Al x Ga1- x )0.52In0.48P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ( $\alpha $ and $\beta $ , respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of Al x Ga1- x As. While both $\alpha $ and $\beta $ initially decrease gradually with increasing bandgap, a sharp decrease in $\beta $ occurs in (Al x Ga1- x )0.52In0.48P when ${x} > 0.61$ , while $\alpha $ decreases only slightly. $\alpha $ and $\beta $ decrease minimally with further increases in ${x}$ and the breakdown voltage saturates. This behavior is broadly similar to that seen in Al x Ga1- x As, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems.

This article investigates the duty-ratio-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) for the dual three-phase drives usually suffers from significant harmonic currents and a large torque ripple. To reduce the harmonic currents, 12 combined voltage vectors are generated and employed as active vectors. Then, the duty-ratio-based ST-DTC is introduced to reduce the torque ripple. Considering that the typical duty-ratio-based ST-DTC exhibits the drawbacks of machine parameter dependent and a certain degree of failure rate in the duty ratio regulation, a simple and effective method taking into account the effect of the machine speed is employed to obtain the duty ratio. Afterward, to prevent the issue of the inverter thermal imbalance caused by using only one type of zero vectors, two types of zero vectors are employed in the switching sequences. With the proposed method, not only the harmonic currents have been suppressed, but also the torque ripple can be considerably reduced, while the merits of the classical ST-DTC such as simple structure and excellent dynamic performance are preserved. The experimental results validate the effectiveness of the proposed strategy.

In this paper, the current distribution of an experimental lead cell is estimated using two methods and the results are compared. Noninvasive measurements are obtained using our magnetic tomography system, consisting of an array of magnetic sensors and a solver algorithm that is specially adapted for application to lead cells. Verification of this magnetic tomography system is achieved by comparing the results with data from a new invasive measurement instrument also reported in this paper. This new instrument is an array of ferrous cored current transducers submerged in the cell electrolyte, providing a direct spatially and temporally resolved measurement of the ionic current in a lead cell. Comparisons between the techniques and data are drawn. The new flowthrough internal sensor array has been designed specifically for this application and represents an improvement over a similar system reported in the literature. In addition, some auxiliary features of the experimental setup are designed to enable useful magnetic measurements to be taken by minimizing the complexity of the setup, and therefore the complexity of the models needed to interpret the data. Example results are presented for a typical automotive lead cell operating at a low state of charge and in a fatigued condition, to demonstrate the ability of both measurement systems to produce spatially and temporally resolved images of current distribution. The methods are evaluated, and the future work is recommended.

Although metals are the most commonly used tooling materials to cure composites, they do not provide optimal results in a microwave environment. Following a selection process based on the properties of the materials, an alternative tooling material in carbon fibre reinforced plastic (CFRP) was successfully utilised to cure CFRP panels in laboratory and industrial microwaves. The conductive carbon fibres in the tool facilitated the fast heat transfer across the part. Other tooling materials including a glass fibre cyanate ester prepreg and tooling board were trialled, although the latter exhibited damage during cure. These advantages demonstrate that the CFRP tool is a compatible material that can be used when microwave curing composites.

This paper investigates the influence of rotor topologies and winding configurations on the electromagnetic performance of 3-phase synchronous reluctance machines with different slot/pole number combinations, e.g. 12-slot/4-pole and 12-slot/8-pole. Transversally laminated synchronous reluctance rotors with both round flux barrier and angled flux barrier have been considered, as well as the doubly-salient rotor as that used in switched reluctance machines. Both concentrated and distributed winding configurations are accounted for, i.e., single layer and double layer conventional and mutually coupled windings, as well as fully-pitched winding. The machine performance in terms of d- and q-axis inductances, on-load torque, copper loss, and iron loss have been investigated using 2-D finite-element analysis. With appropriate rotor topology, 12-slot/4-pole and 12-slot/8-pole machines with fully-pitched and double layer mutually coupled windings can achieve similar torque capacity, which are higher than the machines with other winding configurations. In addition, the synchronous reluctance machine with round flux barrier can have lower iron loss than doubly salient reluctance machine under different working conditions. The prototypes of 12-slot/8-pole single layer and double layer, doubly salient synchronous reluctance machines have been built to validate the predictions in terms of inductances and torques.

This paper investigates the duty-ratio-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) scheme for dual three-phase drives usually suffers from significant harmonic currents and large torque ripple. To reduce the harmonic currents, 12 combined voltage vectors are generated and employed as active vectors. Then, considering that the typical duty-ratio-based ST-DTC exhibits the drawbacks of machine parameter dependent and having failure odds of the duty-ratio regulatory, a simple and effective method taking into account the effect of machine speed is employed to obtain the duty-ratio. With the proposed method, not only the harmonic currents have been suppressed, but also the torque ripple can be considerably reduced, while the merits of classical ST-DTC such as simple structure and excellent dynamic performance are preserved. The experimental results validate the effectiveness of the proposed strategy.

This paper investigates the PWM-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) scheme for dual three-phase drives usually suffers from significant harmonic currents, large torque ripples and variable switching frequency. In this paper, two simple formulae are developed to obtain the amplitude and angle of the torque-production-related reference voltage vectors from the errors of torque and stator flux. To further reduce the harmonic currents caused by machine/inverter asymmetry, harmonic current regulators are employed to generate the harmonic-current-related reference voltage vectors. The specific space vector pulse width modulation (SVPWM) technique is employed to implement the reference voltage vectors. With the proposed method, not only the harmonic currents and torque ripples have been significantly reduced, but also the switching frequency is constant. The experimental results validate the effectiveness of the proposed strategy.

Multiplication and avalanche excess noise measurements have been undertaken on a series of AlInP homo-junction p-i-n and n-i-p diodes with $i$ region widths ranging from 0.04 to 0.89 $\mu \text{m}$ , using 442 and 460 nm wavelength light. Low dark currents of $^{\mathrm {-2}}$ at 95% of breakdown voltage were obtained in all the devices because of its wide bandgap and there was no tunneling dark current present even at high fields >1000 kV/cm. For a given multiplication factor, the excess noise decreased as the avalanche width decreased due to the dead-space effect. Using 460 nm wavelength light, measurements showed that a separate absorption multiplication avalanche photodiode with a nominal multiplication region width of 0.2 $\mu \text{m}$ had an effective $k$ (hole to electron ionization coefficient ratio) of $\sim 0.3$ .

Three-phase nonoverlapping stator wound-field synchronous (NSWFS) machines having salient pole rotors are investigated systematically in this paper. The influence of the rotor pole number on the NSWFS machines is investigated via optimized designs. Using two-dimensional (2-D) finite-element analysis (FEA), the NSWFS machines are found to exhibit higher torque than the nonoverlapping segmented rotor NSWFS (SNSWFS) machines. The FEA-predicted back-electromotive force (EMF), cogging torque, and static torque of the NSWFS machines are validated by experiments on prototype machines.

This paper presents a novel instrumentation system for spatially resolved measurements of steady-state and slowly time-varying magnetic fields. The instrumentation system has a measurement area of $400~{\rm mm}\times 200$ mm consisting of 256 magnetic pixels each measuring the magnetic field crossing the center of the pixel area as three orthogonal vectors. The specified minimum resolution of our chosen sensor is approximately $1.0\times 10^{-7}$ T and the maximum specified measurable magnetic field is $8.0\times 10^{-4}$ T. Magnetic field data can be recorded at approximately one frame per second. This paper also reports the application of this instrumentation system to measurements on lead acid batteries and hybridized battery ultracapacitor combinations. The objective of this paper is to infer, for the first time, the moving charge distribution inside the battery volume by measuring the magnetic field resulting from the moving charge. Empirical tests are reported which show the current distribution as a function of increasing distance down the plate away from the terminal is highly likely to be exponential in nature, with most current flowing in the uppermost portion of the battery.

Dual three-phase electric machine has been attracting increasing interest during the past decades, for its advantages in power segmentation, lower torque pulsations and so on. The conventional switching-table-based direct torque control of dual three-phase permanent magnet synchronous machine drives suffers from large harmonic currents, torque ripple and variable switching frequency. Therefore, a modified deadbeat direct torque control strategy based on space-vector PWM technique is proposed to cope with the aforementioned issues. A simple proportional-integral controller and a dead-time compensator are employed for the further reduction of harmonic currents. The experimental results confirm the effectiveness of the proposed strategy.

This paper presents an analytical study of parasitic oscillation in video bandwidth common base amplifiers. We develop a series of progressively more complex small signal equivalent circuits based on the hybrid-π model [1], [2]. These circuits are developed such that the effect of each new parasitic element on circuit performance is evident. The conditions required for negative input resistance are developed for each equivalent circuit in turn. A general design `rule' of τL

Electrolytic capacitors are an important component within power electronics systems which are known to exhibit poorer reliability compared to other components within the system. In this paper, the changes in electrical parameters (capacitance and equivalent series resistance) which occur as electrolytic capacitors age are characterised at regular intervals over the life of the capacitors. Ageing is observed under three different bias conditions: no bias; constant voltage bias and square wave excitation and at two different ambient temperatures. The data captured within this work presents the changes in capacitor properties from new, reaching to a point which the capacitor parameters have changed sufficiently, such that the capacitor can be considered to have failed. Such data will prove valuable in the development of a system designed to determine the state of health of a capacitor, or could be used to predict its remaining useful lifetime.

A system for measuring, with reduced photocurrent, the excess noise associated with the gain in avalanche photodiodes (APDs), using a transimpedance amplifier front-end and based on phase-sensitive detection is described. The system can reliably measure the excess noise power of devices, even when the un-multiplied photocurrent is low (~10 nA). This is more than one order of magnitude better than previously reported systems and represents a significantly better noise signal to noise ratio. This improvement in performance has been achieved by increasing the value of the feedback resistor and reducing the op-amp bandwidth. The ability to characterise APD performance with such low photocurrents enables the use of low power light sources such as light emitting diode rather than lasers to investigate the APD noise performance.

We report photomultiplication, M, and excess noise, F, measurements at 244nm and 325nm in two 4H-SiC separate absorption and multiplication region avalanche photodiodes (SAM-APDs). Sample A is a 4 x 4 array of 16 SAM-APDs. This structure possesses a relatively thin absorption layer resulting in more mixed injection, and consequently higher noise than sample B. The absorption layer of sample B does not deplete, so 244nm light results in >99% absorption outside the depletion region resulting in very low excess noise. Both structures exhibit very low dark currents and abrupt uniform breakdown at 194V and 624V for samples A and B respectively. Excess noise is treated using a local model [1]. The effective ratio of impact ionisation coefficients (keff) is approximately 0.007, this indicates a significant reduction in the electron impact ionisation coefficient, α, compared to prior work [2-5]. We conclude that the value of α will require modification if thick silicon carbide structures are to fit the local model for multiplication and excess noise.

Minimizing molecular mobility for desiccation preservation of biologics close to ambient temperature using trehalose glasses require quantitative characterization of their enthalpic relaxation at various end water contents. Differential scanning calorimetry (DSC) was used to characterize three different water contents: 0%, 1.5% and 10% over a wide range of aging temperatures. Results showed the characteristic time ( τ ) varies both with the water content and the aging temperature. τ increased with lowered aging temperature but showed a non-monotonous relationship as a function of water content. Fragility of trehalose glasses was analyzed using thermophysical parameters obtained from relaxation studies. The study showed trehalose to be a fragile glass former at all water contents, with 0% water samples showing a relatively stronger glass. A compromise between molecular mobility and glass fragility led to an optimal water content close to 1.5% and an aging temperature close to room temperature. This would ensure a τ value of 9000 h, which corresponds to a storage period of a year.

Recently, a new method has evolved for the recovery of materials in Waste Electrical and Electronic Equipment (WEEE) namely, the repurposing of constituent components for second life. Such an approach is opposed to the traditional raw materials harvesting that is the norm, which in the majority of cases leads to the destruction of serviceable parts together with all other non-recycling materials. This paper presents a novel photovoltaic system suitable for disparate population centres in the developing world utilising repurposed components from discarded computer power supplies.

To date, the recycling process for most Waste Electrical and Electronic Equipment (WEEE) simply involves recovering materials using pyrometallurgy and similar techniques due to the difficultly of removal of their constituent components. Thus most components are incinerated with all other non-recyclable materials. However, for specific types of WEEE an alternative approach has evolved namely the reuse or repurposing of particular parts of the equipment suitable for second life. This paper presents a novel photovoltaic system suitable for disparate population centers in the developing world utilising the ubiquitous ATX computer power supply.

The anomalous behavior of impact ionization in dilute-nitride GaInNAs photodiodes with a range of nitrogen content below 4% is investigated. The ratio of hole- and electron-initiated ionization coefficients, k = β/α, is enhanced by a factor up to ∼4 with increasing nitrogen content. The absolute ionization coefficients are suppressed by up to two orders of magnitude at low electric fields in samples with 3% N. The narrow band gap, suppressed impact ionization, and increased breakdown voltage characteristics of GaInNAs make it a suitable material for use as part of a composite collector in GaAs-based heterojunction bipolar transistors.

This paper proposes and investigates the second life application of computer power supplies for PV applications. The emphasis is on reclamation and reuse of operational power supply components and circuits. Results shown verify operational limits of the power supply validating its suitability for PV-MPPT systems.

This paper reviews the results of 3 years of research and development in optimizing solar project internal rate of return (IRR) through various solar mounting strategies, including fixed-mount, single-axis, and dual-axis tracking. Various tracking algorithms are explored. The results of the research show that shadowing from adjacent photovoltaic (PV) arrays, as well as horizon clouds, significantly impact power output in traditional mounting architectures, but that innovative tracking algorithms and array shape can reduce the negative impact of shadowing. These innovations produce greater power output while reducing project costs and substantially increasing project IRR.

The Republic of China is on the threshold of radical reform of its teacher education system. A comparison to teacher education reform in the U.S.A. will help inform future direction for both nations.

Photomultiplication and excess noise measurements have been undertaken on two 4H-SiC avalanche photodiodes (APDs) using 244-nm light and 325-nm light. The structures are APDs with separate absorption and multiplication regions having multiplication regions of 2.74 and 0.58 μm , respectively. Pure injection conditions in the thicker device permit the measurement of pure-hole-initiated photomultiplication and an excess noise factor. Ionization coefficients for both carrier types have been extracted from these data using a local model. The use of the excess noise factor to infer the value of the less readily ionizing coefficient α from pure hole injection measurements is more robust than direct extraction from mixed injection measurements. This is because mixed injection introduces uncertainty in the generation profile. We report a significant reduction of the electron ionization coefficient α at low fields. The more readily ionizing hole coefficient β remains very similar to prior work.

The avalanche photodiode (APD) is widely used in optical fibre communications (Campbell, 2007) due to its ability to achieve high internal gain at relatively high speeds and low excess noise (Wei et al., 2002), thus improving the system signal-to-noise ratio. Its internal mechanism of gain or avalanche multiplication is a result of successive impact ionisation events. In an optical receiver system, the advantage of internal gain, in the APD, is experienced when the amplifier noise dominates that of a unity-gain photodiode. This increases the signal-to-noise ratio (SNR) and ultimately improves the receiver sensitivity as the gain increases until the APD noise rises to become dominant. Indium Phosphide (InP) is widely used as the multiplication layer material in commercially available APDs for applications in the 0.9–1.7μm wavelength region with In0.53Ga0.47As grown lattice-matched to it as the absorption layer. It has been predicted that Indium Alluminium Arsenide (In0.52Al0.48As) will replace InP, as a more favourable multiplication layer material due to its lower excess noise characteristics (Kinsey et al., 2000). In comparison to InP, tunnelling currents remain lower in InAlAs due to its larger bandgap. While holes ionise more readily than electrons in InP, the opposite holds true for InAlAs and InGaAs, as electrons ionise more readily than holes; thus making the InGaAs/InAlAs combination superior to InGaAs/InP in a SAM APD, in terms of lower excess noise, higher gain-bandwidth product, and improved sensitivity. Studies have also shown that the breakdown voltage of InAlAs APDs is less temperature dependent compared to InP (Tan et al., 2010), which would be useful in temperature sensitive applications, thus making temperature control less critical. The sensitivity performance criterion for digital receivers is its bit-error rate (BER), which is the probability of an error in the bit-identification by the receiver. The receiver sensitivity is defined as the minimum average optical power to operate at a certain BER; 10-12 being a common standard for digital optical receivers. The sensitivity of APD-based high speed optical receivers is governed by three main competing factors, namely the excess noise, avalanche-buildup time and dark current of the APD. Generally, the excess noise and avalanche-buildup time increases with APD gain. Thus, for a fixed multiplication layer thickness, there is a sensitivity-optimised gain that offers a balance between SNR while keeping the degrading contributions from the excess noise factor and intersymbolinterference (ISI) at a minimum. More importantly, changing the thickness of the multiplication layer strongly affects the receiver sensitivity, as the aforementioned three

Trehalose has been shown to be an effective biostabilizer, one explanation for this is that it can easily form glass at near ambient temperatures. Enthalpic relaxation is a physical aging process that occurs in glasses held near, but below, their Tg and is an indicator of the amount of molecular mobility of a particular glass. Since molecular mobility is key to long-term storage biologics in a glassy matrix this study was developed to gain a fundamental understanding of the enthalpic relaxation kinetics of trehalose-water glasses. Through the use of DSC, enthalpic peaks were quantitatively measured for water-trehalose glasses as a function of aging time and aging temperature for three different mass percentages (Mwater /Mtrehalose %, ~0%, ~1.5%, & ~10%). From this data the total amount of relaxation and the relaxation time have been determined using the Cowie-Ferguson equation. Understanding the effects of water on enthalpic relaxation kinetics will help lead to optimized drying protocols and storage parameters.Copyright © 2004 by ASME

This paper reports a novel and versatile system for measuring excess noise and multiplication in avalanche photodiodes (APDs), using a bipolar junction transistor based transimpedance amplifier front-end and based on phase-sensitive detection, which permits accurate measurement in the presence of a high dark current. The system can reliably measure the excess noise factor of devices with capacitance up to 5 nF. This system has been used to measure thin, large area Si pin APDs and the resulting data are in good agreement with measurements of the same devices obtained from a different noise measurement system which will be reported separately.

The ADC-500 is a new blood cell differential classifier manufactured by Abbott Laboratories. It performs 500-cell leukocyte differentials on both normal and abnormal cells, evaluates red cell morphology and estimates platelet sufficiency at a rate of 40 to 50 samples per hour in stand-alone operation. The ADC-500 system consists of a spinner which prepares a uniform blood monolayer on a slide, a stainer which reproducibly stains the slide with Wright's stain, an encoder which attaches an instrument and human readable identification to the slide and an analyzer which accepts a stack of up to 50 slides, evaluates these slides and prints the results and the slide identification on report forms. The system's analysis rate, which represents a 5- to 10-fold increase over other commercially available differential counters, requires a number of specialized techniques for its realization. One key to this performance is the development of a high speed X-Y slide positioning stage which can move to a new cell and settle in 50 msec. Another is the high degree of parallelism used in the system structure and the pipelining of the data processing. A third is the development of uniform and repeatable sample preparation modules. Within the analyzer module, the autofocus, white cell acquisition and high resolution cell analysis systems are independent and operate in parallel. At the same time within the high resolution cell analysis system, one cell is acquired; the digitized image of a second processed; and a third is classified using pattern recognition techniques. All of these tasks, except focus, are under the control of a minicomputer system. Tests of the system reveal good accuracy and an improvement in precision due to the increase in the number of counted cells.