A discrete-time approach to the steady state analysis and optimization of non-linear autonomous circuits

In this paper a method for the steady state analysis and optimization of non-linear autonomous circuits is described. After discretizing the linear part of the circuit, a system of non-linear algebraic equations is obtained. the final formulation is written entirely in the discrete-time domain, making it unnecessary to repeatedly take direct and inverse DFTs during the solution process. Furthermore, it is shown that the resulting formulation may be viewed as a generalization of the harmonic balance equations. an analytic method for computing the exact partial derivatives of the resulting equations with respect to the samples of the variables, the oscillation period and the circuit element values is described, making the proposed approach efficient for both analysis and optimization. Different globally convergent techniques for solving the non-linear system of equations are described, with emphasis on an algorithm based on fast simulated diffusion. Selected application examples are provided to validate the proposed approach.     

Sulphuric acid etching of polyethylene surfaces

The sulphuric acid etching of polyethylene results in the formation of sulphonic groups, varying the surface properties. The study of the groups formed during the etching has been carried out by means of frustrated multiple internal reflection infrared spectroscopy (FMIR). Densities, thermal properties, superficial resistances and resistivities have been correlated with the content of sulphonic groups and treatment time. Moreover, the critical surface tension and platelet adhesion have been examined and related with the change in those properties. Direct sulphonation of polyethylene is a suitable method to change its surface properties, improving the application of this polymer as a biomaterial.     

Mineralization of salicylic acid in acidic aqueous medium by electrochemical advanced oxidation processes using platinum and boron-doped diamond as anode and cathodically generated hydrogen peroxide

Solutions containing 164 mg L(-1) salicylic acid of pH 3.0 have been degraded by electrochemical advanced oxidation processes such as anodic oxidation, anodic oxidation with electrogenerated H(2)O(2), electro-Fenton, photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Their oxidation power has been comparatively studied in a one-compartment cell with a Pt or boron-doped diamond (BDD) anode and a graphite or O(2)-diffusion cathode. In the three latter procedures, 0.5mM Fe(2+) is added to the solution to form hydroxyl radical (()OH) from Fenton's reaction between Fe(2+) and H(2)O(2) generated at the O(2)-diffusion cathode. Total mineralization is attained for all methods with BDD and for photoelectro-Fenton and solar photoelectro-Fenton with Pt. The poor decontamination achieved in anodic oxidation and electro-Fenton with Pt is explained by the slow removal of most pollutants by ()OH formed from water oxidation at the Pt anode in comparison to their quick destruction with ()OH produced at BDD. ()OH generated from Fenton's reaction oxidizes rapidly all aromatic pollutants, but it cannot destroy final Fe(III)-oxalate complexes. Solar photoelectro-Fenton treatments always yield quicker degradation rate due to the very fast photodecarboxylation of these complexes by UVA irradiation supplied by solar light. The effect of current density on the degradation rate, efficiency and energy cost of all methods is examined. The salicylic acid decay always follows a pseudo-first-order kinetics. 2,3-Dihydroxybenzoic, 2,5-dihydroxybenzoic, 2,6-dihydroxybenzoic, alpha-ketoglutaric, glycolic, glyoxylic, maleic, fumaric, malic, tartronic and oxalic acids are detected as oxidation products. A general reaction sequence for salicylic acid mineralization considering all these intermediates is proposed.     

Consequences of using estimated response values from negligible interactions in factorial designs

This article analyzes the increase in the probability of committing type I and type II errors in assessing the significance of the effects when some properly selected runs have not been carried out, and their responses have been estimated from the interactions considered null from scratch. This is done by simulating the responses from known models that represent a wide variety of practical situations that the experimenter will encounter; the responses considered to be missing are then estimated, and the significance of the effects is assessed. Through comparison with the parameters of the model, the errors are then identified. To assess the significance of the effects when there are missing values, the Box‐Meyer method has been used. The conclusions are that one missing value in eight run designs, and up to three missing values in 16 run designs experiments can be estimated without hardly any notable increase in the probability of error when assessing the significance of the effects.     

Saving runs in fractional factorial designs

When it is known a priori that some contrasts are negligible in a factorial design, their expressions can be used to deduce the missing results. In this article we propose a method for using this procedure when, as in the case of fractional designs, it is not known which contrasts will be null. The method is based on first establishing an interval of possible values corresponding to each of the missing results, then identifying which contrasts are always null independently of the value of said results.     

Silicon‐Based Laser Desorption Ionization Mass Spectrometry for the Analysis of Biomolecules: A Progress Report

Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) is widely used in the biomedical field for the label‐free analysis of molecules such as drugs, lipids, peptides, proteins, and biological tissues for molecular imaging. However, organic matrices used in traditional MALDI‐MS applications introduce excessive interferences in the low m/z range. For this reason, nanostructured materials—and in particular silicon‐based LDI strategies—have become a promising alternative, since they provide a much weaker background. Herein, the recent developments in fabrication, functionalization, and practical applications of silicon‐based LDI‐MS methods are reviewed. Also the basic requirements of silicon‐based substrates for optimal LDI analysis by providing an overview of the LDI mechanisms that use silicon‐based substrates instead of organic matrices are reported. Finally, the considerable potential of silicon‐based substrates is discussed, giving suggestions for topics for future research.     

A continuous-time delta-sigma ADC for portable ultrasound scanners

A fully differential fourth-order 1-bit continuous-time delta-sigma ADC designed in a 65 nm process for portable ultrasound scanners is presented in this paper. The circuit design, implementation and measurements on the fabricated die are shown. The loop filter consists of RC-integrators, programmable capacitor arrays, resistors and voltage feedback DACs. The quantizer contains a pulse generator, a high-speed clocked comparator and a pull-down clocked latch to ensure constant delay in the feedback loop. Using this implementation, a small and low-power solution required for portable ultrasound scanner applications is achieved. The converter has a supply voltage of 1.2 V, a bandwidth of 10 MHz and an oversampling ratio of 16 leading to an operating frequency of 320 MHz. The design occupies a die area of \(0.0175\hbox { mm}^2\). Simulations with extracted parasitics show a SNR of 45.2 dB and a current consumption of \(489 \,\upmu \hbox {A}\). However, by adding a model of the measurement setup used, the performance degrades to 42.1 dB. The measured SNR and current consumption are 41.6 dB and \(495\,\upmu \hbox {A}\), which closely fit with the expected simulations. Several dies have been measured, and an estimation of the die spread distribution is given.     

Blocking versus robustness in industrial contexts

The paper discusses the similarities and differences between blocking factors (blocked designs) and noise factors (robust designs) in industrial two‐level factorial experiments. The discussion covers from the objectives of both design types and the nature of blocking and noise factors to the types of designs and the assumptions needed in each case. The conclusions are as follows: the nature and characteristics of noise and blocking factors are equal or very similar; the designs used in both situations are also similar; and the main differences lie in the assumptions and the objectives. The paper argues that the objectives are not in conflict and can easily be harmonized. In consequence, we argue in favor of a unified approach that would clarify the issue, especially for students and practitioners.     

Correlation dimension analysis of heart rate variability in patients with dilated cardiomyopathy

A correlation dimension analysis of heart rate variability (HRV) was applied to a group of 55 patients with dilated cardiomyopathy (DCM) and 55 healthy subjects as controls. The 24-h RR time series for each subject was divided into segments of 10,000 beats to determine the correlation dimension (CD) per segment. A study of the influence of the time delay (lag) in the calculation of CD was performed. Good discrimination between both groups (p<0.005) was obtained with lag values of 5 or greater. CD values of DCM patients (8.4+/-1.9) were significantly lower than CD values for controls (9.5+/-1.9). An analysis of CD values of HRV showed that for healthy people, CD night values (10.6+/-1.8) were significant greater than CD day values (9.2+/-1.9), revealing a circadian rhythm. In DCM patients, this circadian rhythm was lost and there were no differences between CD values in day (8.8+/-2.4) and night (8.9+/-2.1).     

Microhardness and DSC measurements on liquid crystalline poly(diethylene glycolp,p′-bibenzoate) as a function of the ageing time

Summary The ageing process of the liquid crystalline glass of poly(diethylene glycolp,p-bibenzoate), PDEB, has been studied by differential scanning calorimetry and microhardness measurements. The experiments have been performed on a sample of PDEB aged at 36±C during different times. The process was found to be rather fast at that temperature, and the results from both techniques are compared.