Lock-in amplifier error prediction and correction in frequency sweep measurements

This article proposes an analytical algorithm for predicting errors in lock-in amplifiers (LIAs) working with time-varying reference frequency. Furthermore, a simple method for correcting such errors is presented. The reference frequency can be swept in order to measure the frequency response of a system within a given spectrum. The continuous variation of the reference frequency produces a measurement error that depends on three factors: the sweep speed, the LIA low-pass filters, and the frequency response of the measured system. The proposed error prediction algorithm is based on the final value theorem of the Laplace transform. The correction method uses a double-sweep measurement. A mathematical analysis is presented and validated with computational simulations and experimental measurements.     

Thiophene‐ and silarylene‐containing polyesters. Resonance effect on conductivity after polarization in an external electric field

Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (¹H, ¹³C, 135‐DEPT and ²⁹Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 10⁵–2 × 10⁵, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between ? 78 and ? 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm^?1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry     

LaNi5 hydride powder flowability as a function of activation and hydrogen content

Volume expansion of hydrogen absorbing materials, together with inter-particle friction can cause tension accumulation in hydride containers during absorption. When hydride particles absorb hydrogen there is an important volume increase, in the order of 25%. Particles have to accommodate to the container geometry but this movement is opposed by inter-particle friction. Under certain conditions tensions can build up, compromising the mechanical integrity of the container. This phenomenon needs to be addressed at the design stage to avoid mechanical failure of the container.Flow behavior of powder materials is a relevant technological field, usually addressed by means of qualitative or quantitative flowability measuring devices. The rotating drum technique, while mainly qualitative, is well established and can be modified into a completely sealed unit. To determine the flowability of a hydride under different activation stages and hydrogen content levels we developed a rotating drum device that can be pressurized with hydrogen or depressurized. We report particle size evolution and flowability measurements of a hydrogen absorbing material (LaNi₅) at different stages of activation for both absorbed and desorbed states. The results of the present study show that the flowability of LaNi₅ in more dependent on the degree of activation of the sample than on hydrogen absorption state.     

Structural symmetry breaking of silicon‐containing poly(amide‐imide) oligomers and its relation to electrical conductivity and Raman‐active vibrations

Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl₂ and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (¹H, ¹³C, ²⁹Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry     

Survival of Listeria innocua in Minas Traditional Serro cheese during ripening

Cheese produced with raw milk can be a risk to consumer health. It is known that lactic acid bacteria present in raw milk and in natural starters can produce antimicrobial compounds against some foodborne bacteria. This work aimed to evaluate the survival of Listeria innocua in Minas Traditional Serro cheese during cheese ripening. The cheeses were inoculated with 10¹, 10² or 10³ CFU mL⁻¹ of the bacterium and were analyzed for 60 days of ripening at 30 °C. It was observed that the time and the dose of bacteria inoculated affected (p < 0.05) the survival of L. innocua. Even when the lowest dose was inoculated, at the end of the 60 days, approximately 10² CFU mL⁻¹ of L. innocua was detected in the cheese. The lactic acid bacteria present in the milk and in the natural starter were not sufficient to guarantee the absence of L. innocua in Minas Traditional Serro cheese even after 60 days of storage, as is required by Brazilian legislation.     

Legacy code and parallel computing: updating and parallelizing a numerical model

In this paper, we present several important details in the process of legacy code parallelization, mostly related to the problem of maintaining numerical output of a legacy code while obtaining a balanced workload for parallel processing. Since we maintained the non-uniform mesh imposed by the original finite element code, we have to develop a specially designed data distribution among processors so that data restrictions are met in the finite element method. In particular, we introduce a data distribution method that is initially used in shared memory parallel processing and obtain better performance than the previous parallel program version. Besides, this method can be extended to other parallel platforms such as distributed memory parallel computers. We present results including several problems related to performance profiling on different (development and production) parallel platforms. The use of new and old parallel computing architectures leads to different behavior of the same code, which in all cases provides better performance in multiprocessor hardware.

     

Some factors affecting delayed ettringite formation in heat-cured mortars

Although more than 10 years of studies on delayed ettringite formation (DEF) have led to consensus in numerous areas of past disagreements, some questions remain experimental work is needed to complete the knowledge of this pathology. Following this objective, this paper studies the influence of pre-existing microcracking, wetting/drying cycles and the type of sulfated addition on DEF in steam cured mortars. The mortar specimens were prepared using an Ordinary Portland Cement and two types of sulfate were added to the mixtures: calcium sulfate (CaSO₄) or sodium sulfate (Na₂SO₄). The results confirm the well-known effect of temperature: no expansion was observed in any of the mixtures cured at room temperature. Moreover, no expansion was observed after 800 days for the reference mortar or for the mortar containing calcium sulfate but all the specimens of heat-cured mortars containing sodium sulfate expanded markedly after about 50 days whatever the supplementary treatments applied (thermal shrinkage or wetting/drying cycles). These results show the significant role played by alkalis in the occurrence of delayed ettringite. The supplementary treatments intended to cause prelimiray microcracking of the specimens did not promote expansion but contributed to a slight acceleration of the reaction. The ultimate values of expansion were similar to those obtained with sound mortars.     

Diabetic nephropathy,autophagy and proximal tubule protein endocytic transport: A potentially harmful relationship

Diabetic nephropathy (DN) is the most frequent cause of chronic renal failure. Until now, the pathophysiological mechanisms that determine its development and progression have not yet been elucidated. In the present study, we evaluate the role of autophagy at early stages of DN, induced in type 2 diabetes mellitus (T2DM) mouse, and its association with proximal tubule membrane endocytic receptors, megalin and cubilin. In T2DM animals we observed a tubule-interstitial injury with significantly increased levels of urinary GGT and ALP, but an absence of tubulointerstitial fibrosis. Kidney proximal tubule cells of T2DM animals showed autophagic vesicles larger than those observed in the control group, and an increase in the number of these vesicles marked with LBPA by immunofluorescence. Furthermore, a significant decrease in the ratio of LC3II/LC3I isoforms and in p62 protein expression in DN affected animals is shown. Finally, we observed a marked increase in urinary albumin and vitamin D binding-protein levels in T2DM animals as well as a significant decrease in expression of megalin in the renal cortex. These results indicate an alteration of the tubular endocytic transporters in DN, which could be related to autophagic dysfunction, which would in turn result in impaired organelle recycling, thus contributing to the progression of this disease.     

Easy classification of traditional Minas cheeses using artificial neural networks and discriminant analysis

The classification of traditional Minas cheese (TMC) from different regions is important to ensure authenticity. Different chemometric approaches were used to discriminate TMCs from three different regions (Serro, Canastra and Araxá) of Minas Gerais, Brazil. The data obtained from the literature were used to develop an artificial neural network and to obtain linear discriminant functions, which were able to classify 100% of cheeses from different regions as a function of physico‐chemical composition. Both chemometric methods can be very useful tools to discriminate TMC from different regions based on physico‐chemical data which are obtained in a very quick and simple way.