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.     

Nanostructure characterization of high k materials by spectroscopic ellipsometry

In this work, the optical and structural properties of high k materials such as tantalum oxide and titanium oxide were studied by spectroscopic ellipsometry, where a Tauc-Lorentz dispersion model based in one (amorphous films) or two oscillators (microcrystalline films) was used. The samples were deposited at room temperature by radio frequency magnetron sputtering and then annealed at temperatures from 100 to 500 °C. Concerning the tantalum oxide films, the increase of the annealing temperature, up to 500 °C does not change the amorphous nature of the films, increasing, however, their density. The same does not happen with the titanium oxide films that are microcrystalline, even when deposited at room temperature. Data concerning the use of a four-layer model based on one and two Tauc-Lorentz dispersions is also discussed, emphasizing its use for the detection of an amorphous incubation layer, normally present on microcrystalline films grown by sputtering.     

Performance Evaluation of Packet Mobile Communications through Level Crossing Analysis

In this paper the performance of a packet mobile radio network is studied inthe presence of shadow fading outage intervals.Under quite general assumptions for the medium access protocol,the probability mass function of the sequence of packets that may be lostdue to an outage interval is derived. It is seen that long sequences of lostpackets are likely to occur for typical values of the mobile speed andshadowing correlation parameters.For delay constrained sources, e.g., voice, the analysis is mainly focused atderiving the probability function of the sequence of dropped packetsand the probability of dropping. For data sources, the delay statistic isalso derived. In the latter case, the effect of finite buffer length isaddressed. Simulation is used to verify the accuracy of approximations introduced in the analysis.     

Existence of 3D-Vortices in Abelian Gauge Theories

We consider the Abelian gauge theory related to the interaction between the solitary waves of the nonlinear Klein-Gordon equation and the electromagnetic field. We analyze the existence of electromagnetostatic solutions and, in particular, of vortices. Dedicated to the memory of Professor Aldo Cossu     

Hot carrier-induced degradation of gate overlapped lightly dopeddrain (GOLDD) polysilicon TFTs

Hot-carrier injection is known to produce interface states and oxide trapped charge, which, depending upon their spatial distribution, can strongly influence the local electric fields as well as the current flow. In this work, we analyze the hot carrier-induced degradation of gate overlapped lightly doped drain (GOLDD) polysilicon thin film transistors (TFTs) and a new model, which correlates the interface state generation with the hot carrier injection current, is proposed. The defect generation rate has been assumed to depend upon the product of hot electron and hole currents J_eh, and the resulting interface state distribution has been evaluated self-consistently with the current density and carrier concentration distributions. By successive iterations, a complete spatial and time evolution of the interface state distribution has been determined, and the electrical characteristics, calculated with these interface state distributions are in good agreement with the experimental data     

Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.     

Synthesis of 1,2-dihydroindolo [1,7-AB] [1,5] benzodiazepines and related structures. A new heterocyclic ring system

The synthesis of the novel 1,2-dihydroindolo [1,7-ab][1,5]benzodiazepine ring system 4 is described. Condensation of 2-fluoronitrobenzene with indoline provided the starting material for the synthesis, 1-(2-nitrophenyl)indoline (1a) in high yield. The nitro group was reduced catalytically and the resulting amino function was acylated to afford the heterocycle percursor amide 3. Refluxing this amide in phosphorus oxychloride brought about a Bischler-Napieralski type cyclodehydration to form the target 1,2-dihydroindolo[1,7-ab][1,5]benzodiazepine ring system. Dehydrogenation of the latter led to the fully aromatic indolo[1,7-ab][1,5]benzodiazepine structure 5, while reduction with sodium borohydride provided the 1,2,6,7-tetrahydroindolo[1,7-ab]-[1,5]benzodiazepine tetracycle 6.     

Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer

A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1×10^–7 mg mL^–1 up to 1x10^–3 mg mL^–1 [correlation coefficient (r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL^–1). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement.     

Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin

Supercritical carbon dioxide (scCO₂)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO₂ as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD).     

Adsorption mechanism of polylysine on hydroxyapatite and its effect on dissolution properties of hydroxyapatite

Adsorbed amounts of poly-l-lysine (pLys) and bromide ion on hydroxyapatite (HAp) from aqueous solutions of poly-l-lysine hydrobromide, and amounts of calcium and phosphate ions liberated concurrently from HAp during the adsorption of pLys were determined at 25 degrees . The pLys was adsorbed on HAp by the mechanism of ion-exchange between its amino groups and calcium ions of HAp. The released amount of calcium ion increased, therefore, with the adsorbed amount of pLys. On the other hand, the released amount of phosphate ion first decreased and then increased after attaining a minimum with the equilibrium concentration of pLys. The analysis using an equilibrium dialysis method revealed that the released phosphate ions were mainly in the bound state to the amino groups of pLys remaining in the solution, and that the concentrations of calcium and phosphate ions free from both HAp and pLys were restricted by each other under the law of the solubility product of HAp. The first decrease in the released amount of phosphate ion was concluded to be attributed primarily to the increase in the released amount of calcium ion because pLys remaining in the solution was little in this region. When sodium hydroxide was added to the solution, the adsorbed amount of pLys increased and then slightly decreased with the equilibrium pH of the solution due to the increase or decrease of the electrostatic attractive force between the adsorbate and the adsorbent. However, conformational change in pLys around pH 10 seemed to have little effect on the adsorption.