A multiwinding modeling method for high frequency transformers and inductors

This paper presents a method to obtain an electric model for transformers and inductors, including both frequency and geometry effects in the windings, which can be linked with existing core models. One-dimensional distributions for magnetic and electric fields are assumed, and from Maxwell's equations an equivalent electric circuit is easily obtained. This equivalent circuit has been included in analog simulators (Spice, AnalogWorkBench, Saber ...), and comparisons between measured and simulated results are shown, both in time domain and in AC sweep, which verify the model accuracy. The model described in this paper allows designers to deal with key issues in the design of high-frequency magnetic components (copper losses, leakage inductance, skin and proximity effects) by using analog simulators, which are usually more familiar to them than finite-element analysis tools.     

Thick-film hybrid technology for low-output-voltage DC/DC converter

The new requirements in portable and telecommunication equipment also affect the supply systems. The current tendency to lower the output voltage (3.3, 2.7 V/sub DC/) together with the necessity of an important size reduction is modifying the strategies for dc/dc converter implementation. Low-voltage high-power-density applications present two important factors that must be analyzed: thermal problems due to high power density, and the high currents to be handled. This paper presents a 10-W dc/dc buck converter with passive integration using hybrid technology (within the frame of ESPRIT Project 23910.). As a result of the mentioned integration technique, a power density of 6.25 W/cm/sup 3/ was obtained with high efficiency (approximately 90%).     

Component-Based Derivation of a Parallel Stiff ODE Solver Implemented in a Cluster of Computers

A component-based methodological approach to derive distributed implementations of parallel ODE solvers is proposed. The proposal is based on the incorporation of explicit constructs for performance polymorphism into a methodology to derive group parallel programs of numerical methods from SPMD modules. These constructs enable the structuring of the derivation process into clearly defined steps, each one associated with a different type of optimization. The approach makes possible to obtain a flexible tuning of a parallel ODE solver for several execution contexts and applications. Following this methodological approach, a relevant parallel numerical scheme for solving stiff ODES has been optimized and implemented on a PC cluster. This numerical scheme is obtained from a Radau IIA Implicit Runge–Kutta method and exhibits a high degree of potential parallelism. Several numerical experiments have been performed by using several test problems with different structural characteristics. These experiments show satisfactory speedup results.     

The determination of the boundaries between continuous anddiscontinuous conduction modes in PWM DC-to-DC converters used as powerfactor preregulators

The determination of the boundaries between both modes of conduction (continuous and discontinuous) in PWM DC-to-DC switching power converters used as power factor preregulators (PFP) is presented in this paper. When a DC-to-DC switching power converter works as a power factor preregulator, its operating point is constantly changing due to the fact that both the DC voltage conversion ratio and the load “seen” by the power converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). In these conditions, the conduction mode cannot be directly determined. In this paper, the boundaries between both conduction modes in each angle of the half-sinusoidal input voltage have been determined. The conditions to always operate in continuous or in discontinuous conduction modes have been determined as well. Finally, these results have been verified by simulations and experimental results     

A new control strategy for an AC/DC converter based on a piezoelectric transformer

Piezoelectric transformers (PTs) are an attractive solution to reduce size and weight in ac/dc converters. In this paper, a PT-based topology is presented together with a control method. As an application, an 8-W ac/dc adapter (110 V/sub AC/ input, 12 V/sub DC/ output) is presented operating at frequencies around 500 kHz.     

Zinc coating control on steel wires

Galvanic steel wire manufacturers have to fulfill several international regulations regarding zinc mass by surface unit. This article presents a new sensor to measure this parameter online. Details about the different parts of the system (sensor, circuitry, adjustment, and signal processing) are explained. Experimental results in a real manufacturing line are also presented. Online measurement conserves zinc mass and guarantees savings     

Ptuba: a tool for the visualization of helix surfaces in proteins

Projection of transmembrane helices using a Uniform B-spline Algorithm is a tool for the visualization of interactions between helices in membrane proteins. It allows the user to generate projections of 3D helices, no matter what their deviations from a canonical helix might be. When associated with adapted coloring schemes it facilitates the comprehension of helix-helix interactions. Examples of transmembrane proteins were chosen to illustrate the advantages that this method provides. In the glycophorin A dimer we can easily appreciate the structural features behind homodimerisation. Using the structure of the fumarate reductase we analyze the contact surfaces inside a helical bundle and thanks to structures from a molecular dynamics simulation we see how modifications in structure and electrostatics relate to their interaction. We propose the use of this tool as an aid to the visualization and analysis of transmembrane helix surfaces and properties.     

Effects of the level and duration of maternal diets with negative dietary cation-anion differences prepartum on calf growth,immunity, and mineral and energy metabolism

The objectives were to investigate the effects that maternal diets containing negative dietary cation-anion differences (DCAD) fed in the last 42 d of gestation may have on the acid–base status, hematology, mineral and energy metabolism, growth, and health of calves. The experiment was a randomized block design with a 2 × 2 factorial arrangement of 2 levels of negative DCAD (?70 or ?180 mEq/kg) and 2 feeding durations (the last 21 d prepartum and the last 42 d prepartum). Bulls and heifers (n = 60) born to these dams were weighted at birth and fed 3.8 L of colostrum for their first feeding, and only heifers (n = 44, 9–12/treatment) were kept thereafter. Heifer body weight was also recorded at 21 d, 42 d, 62 d, 3 mo, and 6 mo of age. Blood was collected at birth, before colostrum feeding, and at 1, 2, 3, 21, and 42 d of age and assayed for minerals, metabolites, and cell counts. Heifers born to dams fed the last 42 d prepartum weighed 2.8 and 4.8 kg less at birth and 62 d, respectively, compared with calves born to dams fed the last 21 d prepartum; however, body weight at 3 and 6 mo of age was similar. Concentrations of ionized calcium did not differ among treatments at birth, but heifers born to ?180 DCAD dams had increased blood concentrations at 3 d of age, whereas those born to ?70 DCAD dams did not. At birth, heifers born to ?180 DCAD dams experienced a subtle and transient metabolic acidosis (pH = 7.33 ± 0.02; pCO₂ = 53.0 ± 2.4 mmHg; HCO₃^? = 27.6 ± 0.7 mmol/L) compared with the more evident metabolic acidosis observed in those born to ?70 DCAD cows (pH = 7.28 ± 0.02; pCO₂ = 59.3 ± 2.4 mmHg; HCO₃^? = 27.8 ± 0.7 mmol/L). Heifers born to ?180 DCAD dams had reduced concentrations of β-hydroxybutric acid and nonesterified fatty acids compared with those born to ?70 DCAD dams. Efficiency of IgG transfer from colostrum into blood and serum concentrations did not differ among treatments. There was no relationship between measures of metabolic acidosis and measures of efficiency of IgG absorption. Percentage of lymphocytes and neutrophils was altered by maternal treatments; however, treatments did not affect calf morbidity. Extending the duration of feeding up to 42 d or reducing the level of negative DCAD to ?180 mEq/kg in maternal diets exerted a transient metabolic acidosis in the calves and slightly affected measures of mineral, energy metabolism, and growth.     

Magnetism in V-Doped Tio2 Bulk Samples

Bulk samples of Ti_1?x V _x O₂ nominal composition with x=0.08 were fabricated with the standard solid-state reaction. Appropriate proportions of Titanium dioxide (TiO₂) and vanadium pentoxide (V₂O₅) high-purity powders were thoroughly mixed according to the desired stoichiometry. The solid-state reaction was conducted for 30?min. Pellets were formed applying 8 tons of pressure. Then, they were subjected to thermal process at 550?°C for 10?h in air. The samples were characterized by X-ray diffraction analysis. Magnetic properties were studied by measuring magnetization as a function of temperature and applied magnetic fields. Magnetization as a function of temperature without applied magnetic field showed that magnetization increases slowly with decreasing temperature from 300 to 42?K, but for temperatures below 42?K, it increases rapidly. Magnetization as a function of the applied magnetic field, at 5, 77, and 300?K revealed the ferromagnetic behavior of the samples.     

Use of calcitriol to maintain postpartum blood calcium and improve immune function in dairy cows

Our objectives were to determine the effects of an injectable formulation of calcitriol on mineral metabolism and immune function in postpartum Holstein cows that received an acidogenic diet prepartum to minimize hypocalcemia. In experiment 1, cows within 6 h of calving received calcitriol (0, 200, or 300 μg) to determine the dose needed to increase plasma concentrations of Ca; 300 μg was sufficient to sustain Ca for at least 3 d. In experiment 2, multiparous cows were assigned randomly to receive only vehicle (control, n = 25) or 300 μg of calcitriol (n = 25) subcutaneously within the first 6 h after calving. Blood was sampled before treatment and 12 h later, then daily until 15 d in milk (DIM), and analyzed for concentrations of ionized Ca (iCa), total Ca (tCa), total Mg (tMg), and total P (tP), metabolites, and hormones. Urine was sampled in the first 7 DIM and analyzed for concentrations of tCa, tMg, and creatinine. Neutrophil function was evaluated in the first week postpartum. Dry matter intake and production performance were evaluated for the first 36 DIM. Calcitriol administration increased concentrations of calcitriol in plasma within 12 h of application from 51 to 427 pg/mL, which returned to baseline within 5 d. Concentrations of iCa and tCa increased 24 h after treatment with calcitriol. Concentrations of iCa (control = 1.08 vs. calcitriol = 1.20 mM), tCa (control = 2.23 vs. calcitriol = 2.33 mM), and tP (control = 1.47 vs. calcitriol = 1.81 mM) remained elevated in cows treated with calcitriol until 3, 5, and 7 DIM, respectively, whereas concentration of tMg (control = 0.76 vs. calcitriol = 0.67 mM) was less in calcitriol cows than control cows until 3 DIM. Concentrations of parathyroid hormone decreased in calcitriol cows compared with control cows (control = 441 vs. calcitriol = 336 pg/mL). Calcitriol tended to increase plasma concentrations of β-hydroxybutyrate and serotonin, but concentrations of glucose, nonesterified fatty acids, and C-telopeptide of type I collagen in plasma did not differ between treatments. Cows treated with calcitriol excreted more urinary tCa (control = 0.5 vs. calcitriol = 2.1 g/d) and tMg (control = 4.5 vs. calcitriol = 5.0 g/d) in the first 7 and 2 DIM, respectively, than control cows. Compared with control, calcitriol improved the proportion of neutrophils with oxidative burst (control = 31.9 vs. calcitriol = 40.6%), mean fluorescence intensity for oxidative burst (control = 90,900 vs. calcitriol = 99,746), and mean fluorescence intensity for phagocytosis (control = 23,887 vs. calcitriol = 28,080). Dry matter intake, yields of milk, and milk components did not differ between treatments. Administration of 300 μg of calcitriol at calving was safe and effective in increasing blood concentration of iCa and plasma concentrations of calcitriol, tCa, and tP for the first 6 d after treatment, and improved measures of innate immune function in early-lactation Holstein cows.