Multilevel Converter-Based Dual-Frequency Induction Heating Power Supply

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies have been researched and even commercialized. Dual-frequency power supplies are a significant development for heat-treating workpieces with uneven geometries, such as gears, since different portions of such workpieces are heated dissimilarly at a single frequency and so require a two step process using a single-frequency power supply. On the other hand, a dual-frequency power supply can achieve the desired result for such workpieces in a one step process. However, the existing approaches to dual-frequency voltage generation could be improved to achieve higher efficiency, improved control, reduced electromagnetic interference and greater reliability. This paper proposes the use of multilevel converters for providing induction heating power at two frequencies simultaneously. It also describes how the stepping angles for the desired output from this converter were determined. Furthermore, experimental results are presented as a verification of the analysis

Multilevel Inverter-Based Dual-Frequency Power Supply

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies simultaneously have been introduced and commercialized. These represent a significant development particularly for heat-treating workpieces with uneven geometries, such as gears. Still, the existing approaches to dual-frequency voltage generation could be improved upon to achieve better control, higher efficiency, and reduced electromagnetic interference. This letter proposes the use of multilevel inverters for providing power at two frequencies simultaneously. It describes how the stepping angles for the desired output from such inverters can be determined. Furthermore, experimental results are presented as verification of the concept and to demonstrate the achievement of improved harmonic level control and reduced device switching frequency

Multilevel Inverters with Equal or Unequal Sources for Dual-Frequency Induction Heating

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies have been researched and even commercialized. Dual-frequency power supplies are a significant development for heat-treating workpieces with uneven geometries, such as gears, since different portions of such workpieces are heated dissimilarly at a single frequency and so require a two step process using a single-frequency power supply. On the other hand, a dual-frequency power supply can achieve the desired result for such workpieces in a one step process. This paper proposes the use of multilevel converters for providing induction heating power at two frequencies simultaneously, which may achieve higher efficiency, improved control, reduced electromagnetic interference and greater reliability than existing dual-frequency power supplies. It also describes how the stepping angles for the desired output from such converters can be determined for both the equal and unequal source cases. Furthermore, experimental results are presented as a verification of the analysis

Nanopowder management and control of plasma parameters in electronegative SiH4 plasmas

Management of nanosize powder particles via control of plasma parameters in a low-pressure SiH4 discharge for silicon microfabrication technologies is considered. The spatial profiles of electron and positive/negative ion number densities, electron temperature, and charge of the fine particles are obtained using a self-consistent fluid model of the electronegative plasmas in the parallel plate reactor geometry. The model accounts for variable powder size and number density, powder-charge distribution, local plasma nonuniformity, as well as UV photodetachment of electrons from the nanoparticles. The relations between the equilibrium discharge state and powder properties and the input power and neutral gas pressure are studied. Methods for controlling the electron temperature and SiH3- anion (here assumed to be the powder precursor) density, and hence the powder growth process, are proposed. It is shown that by controlling the neutral gas pressure, input power, and powder size and density, plasma density profiles with high levels of uniformity can be achieved. Management of powder charge distribution is also possible through control of the external parameters

An exploration of the knowledge and attitudes towards breastfeeding among a sample of Chinese mothers in Ireland

<p>Abstract</p> <p>Background</p> <p>Psychological factors are important in influencing breastfeeding practices. This retrospective study explored knowledge and attitudes related to breastfeeding of Chinese mothers living in Ireland.</p> <p>Methods</p> <p>A cross-sectional self-administrated survey written in Chinese was distributed to a convenience sample of 322 immigrant Chinese mothers mainly <it>via </it>Chinese supermarkets and Chinese language schools in Dublin, with the involvement of the snowball method to increase sample size. Maternal breastfeeding knowledge and attitudes were described, their associations with socio-demographic variables were explored by Chi-square analysis, and their independent associations with breastfeeding behaviours were estimated by binary logistic regression analyses.</p> <p>Results</p> <p>In spite of considerable awareness of the advantages of breastfeeding (mean score = 4.03 ± 0.73), some misconceptions (<it>e</it>.<it>g</it>. 'mother should stop breastfeeding if she catches a cold') and negative attitudes (<it>e</it>.<it>g</it>. breastfeeding inconvenient, embarrassing, and adverse to mothers' figure) existed, especially among the less educated mothers. Cultural beliefs concerning the traditional Chinese postpartum diet were prevalent, particularly among those who had lived in Ireland for a shorter duration (P = 0.004). Psychological parameters had strong independent associations with breastfeeding practices in this study. Those who had lower awareness score (OR = 2.98, 95% CI: 1.87-4.73), more misconceptions and negative attitudes (P < 0.05), and weaker cultural beliefs (P < 0.05) were less likely to breastfeed.</p> <p>Conclusions</p> <p>Findings highlight a need to focus resources and education on correcting the misconceptions identified and reversing the negative attitudes towards breastfeeding among Chinese mothers in Ireland, in particular those with primary/secondary level of education. Mothers' cultural beliefs should also be acknowledged and understood by healthcare providers.</p

Changes in muscle-tendon unit length-force characteristics following experimentally induced photothrombotic stroke cannot be explained by changes in muscle belly structure.

Purpose The aim of this study was to assess the effects of experimentally induced photothrombotic stroke on structural and mechanical properties of rat m. flexor carpi ulnaris. Methods Two groups of Young-adult male Sprague–Dawley rats were measured: stroke (n = 9) and control (n = 7). Photothrombotic stroke was induced in the forelimb region of the primary sensorimotor cortex. Four weeks later, muscle–tendon unit and muscle belly length–force characteristics of the m. flexor carpi ulnaris, mechanical interaction with the neighbouring m. palmaris longus, the number of sarcomeres in series within muscle fibres, and the physiological cross-sectional area were measured. Results Stroke resulted in higher force and stiffness of the m. flexor carpi ulnaris at optimum muscle–tendon unit length, but only for the passive conditions. Stroke did not alter the length–force characteristics of m. flexor carpi ulnaris muscle belly, morphological characteristics, and the extent of mechanical interaction with m. palmaris longus muscle. Conclusion The higher passive force and passive stiffness at the muscle–tendon unit level in the absence of changes in structural and mechanical characteristics of the muscle belly indicates that the experimentally induced stroke resulted in an increased stiffness of the tendon