An 8-Bit Digitally Controlled Programmable Phase Shifter Circuit for Sinusoidal Signals with 252∘ Phase Control Range

In this paper, the synthesis, design, and implementation of a programmable phase shifter circuit for sinusoidal signals is presented. The proposed circuit, built-up herein with operational amplifiers (OPAMPs), high precision resistors and low voltage switches, consists of a digitally controlled amplitude attenuator in combination with a single-tone orthogonalizer. Experimental results agree with theoretical background: the attained phase range was 252^° in 256 steps with a median step of 0.9^°. The inaccuracy of the circuit was determined to be of 0.03 %. Contrary to other OPAMP approaches for sinusoidal signals reported in the literature and based on a first-order all-pass filter structure, the approximation suggested in this work is based on a different concept. The achieved results demonstrate the functionality of the system for the case of a sinusoidal signal with frequency of 1 kHz. Notwithstanding, the proposed architecture can be extended to operate at higher frequencies by using different building blocks with larger bandwidth. Furthermore, it can be extended as well to work out with other periodic input waveforms, like triangular shapes or square waves, with the use of an appropriate orthogonalizer.     

Cs Promoted Triglyceride Transesterification Over MgO Nanocatalysts

The influence of Cs on the structure and basicity of nanocrystalline MgO was assessed via electron microscopy, CO₂ chemisorption, XRD and XPS. Caesium incorporation via co-precipitation under supercritical conditions generates Cs₂Mg(CO₃)₂ nanocrystallites with an enhanced density and strength of surface base sites. Wet impregnation proved less effective for modifying MgO nanocrystals. A strong synergy between Cs and Mg components in the co-precipitated material dramatically enhanced the rate of tributyrin transesterification with methanol relative to undoped MgO and homogeneous Cs₂CO₃ catalysts. On-stream deactivation of Cs-doped MgO reflects heavy surface carbon deposition and loss of the high activity Cs₂Mg(CO₃)₂ phase due to limited Cs dissolution.     

Analysis of Cheese Small Molecules by UPLC–QToF-MS and Multivariate Statistical Methods Using Several Extraction Procedures

Lyophylized (L) and nonlyophylized (NL) samples of two cheeses from different batches were extracted with either methanol:water (8:2, v/v) or isopropanol:water (7:3, v/v), and the extracts were analyzed by ultraperformance liquid chromatography coupled with electrospray ionization/quadruple-time-of-flight mass spectrometry (UPLC–ESI–QToF-MS) in both positive and negative modes. Chromatographic and mass spectrometric data were further compared for different samples by paired t test and principal component analysis (PCA). Mass spectra at different elution times were manually checked and major peaks tentatively identified according to their m/z values by search in available databases. A number of gangliosides and polyglycosilated ceramides were found to be the most abundant components. PCA showed samples could be clustered according to extraction procedure and cheese, and paired t test comparison also showed significant (p?<?0.05) differences between L and NL samples extracted with methanol:water. L and NL samples could only be distinguished in PCA when data from the whole chromatographic range were used. Results are discussed based on extraction solvent polarity and feasibility of PCA for comparison of cheese chemical composition after untargeted UPLC–MS analysis.     

Accelerated Aging in 3-mol%-Yttria-Stabilized Tetragonal Zirconia Ceramics Sintered in Reducing Conditions

The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP) ceramics sintered in air and in reducing conditions was investigated at 140°C in water vapor. It was observed by X-ray diffraction (XRD) that 3Y-TZP samples sintered in reducing conditions exhibited significantly higher tetragonal-to-monoclinic transformation than samples with similar density and average grain size values but obtained by sintering in air. This fact is explained by the increase of the oxygen vacancy concentration and by the presence at the grain boundary region of a new aggregate phase formed because of the exolution of Fe²⁺ ions observed by X-ray photoelectron spectroscopy.     

Plasticized nanocomposite polymer electrolytes based on poly(oxyethylene) and cellulose whiskers

Nanocomposite polymer electrolytes based on a plasticized high molecular weight poly(oxyethylene) (POE) reinforced with high aspect ratio cellulose nanoparticles were reported. The influence of tetra(ethylene) glycol dimethyl ether (TEGDME) as plasticizer is investigated. The study mainly focuses on the dynamic mechanical behavior and ionic conductivity performances. The miscibility of the blend POE/TEGDME was investigated using both thermal and mechanical investigations. Viable polymer electrolytes can be obtained from this combination, conciliating acceptable ionic conductivities and outstanding mechanical performances on a large temperature range.     

Anatase and rutile TiO2 thin films prepared by reactive DC sputtering at high deposition rates on glass and flexible polyimide substrates

Titanium oxide thin films have been prepared by reactive DC sputtering at room temperature on soda-lime glass (SLG) and flexible polyimide (Kapton) substrates. The sputtering conditions have been adjusted in order to achieve high deposition rates between 15 and 45 nm/min. Post-deposition heating of the samples has been performed at 350 °C in nitrogen during 30 min. The crystalline structure of these films and their optical, morphological, and electric characteristics have been studied before and after annealing by X-ray diffraction, spectrophotometric measurements, atomic force microscopy, and the four-point probe method. The optical data indicate that pure anatase phase, which crystallizes after the heating process, is obtained on both SLG and Kapton substrates at the lowest deposition rate (15 nm/min). In this case, the samples exhibit high electric resistivity above 300 Ωcm. Otherwise, for the highest deposition rate (45 nm/min), crystalline rutile is identified in the as-grown and heated films, with a lower optical gap energy than anatase and also a lower resistivity that reaches 0.3 Ωcm after heating. At intermediate deposition rates, anatase and rutile coexist in the samples as has been verified by X-ray diffraction, although the overall optical and electric characteristics are dominated by the rutile phase. Analogous titanium oxide layers have been obtained on SLG and Kapton, and this opens the possibility of substituting flexible plastics for conventional glass substrates.     

Ecotaxes and their impact in the cost of steam and electric energy generated by a steam turbine system

Ecotaxes allow the internalization of costs that are considered externalities associated with polluting industrial process emissions to the atmosphere. In this paper, ecotaxes internalize polluting emissions negative impacts that are added to electricity and steam generated costs of a steam turbine and heat recovery systems from a utilities refinery plant. Steam costs were calculated by means of an exergy analysis tool and Aspen Plus simulation models. Ecotaxes were calculated for specific substances emitted in the refinery flue gases, based on a toxicity and pollution scale. Ecotaxes were generated from a model that includes damages produced to biotic and abiotic resources and considers the relative position of those substances in a toxicity and pollution scale. These ecotaxes were internalized by an exergoeconomic analysis resulting in an increase in the cost per kWh produced. This kind of ecotax is not applied in Mexico. The values of ecotaxes used in the cost determination are referred to the values currently applied by some European countries to nitrogen oxides emissions.     

Effect of High Pressure and 4-Hexylresorcinol on Enzymatic Activity and Darkening in Oysters

ABSTRACT: Oysters treated with and without 4-hexylresorcinol were pressurized (400 MPa/7 °C/10 min) and stored chilled for 21 d, either vacuum-packed or packaged aerobically. The results of visual evaluation of darkening and polyphenoloxidase (PPO) activity levels suggest that during storage, non enzymatic browning occurred 1st, followed by blackening caused by PPO activity. PPO activity did not increase in the vacuum-packed oysters during storage, but pressurization was observed to activate the PPO. Autolytic activity in the oysters increased due to the high-pressure treatment, although higher autolysis levels were recorded in the unpressurized oysters at the end of storage. Inhibition of PPO activity by the 4-hexylresorcinol was observed chiefly in the vacuum-packed batches.     

Quercetin properties as a functional ingredient in omega‐3 enriched fish gels fed to rats

Wistar rats were fed with surimi gels containing either sunflower oil, fish oil (ω3), and the same formulation additionally supplemented with 1.05 g kg⁻¹ quercetin (ω3‐Q). Antioxidant capacity was highest in gels with added quercetin when measured by the ferric‐reducing/antioxidant power (FRAP) method, but not by the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical assay. Lipid stability was not enhanced by quercetin since commercial fish oil already contains stabilizers. Quercetin modified neither rheological properties nor water‐holding capacity of the gels; however, it produced a large increase in yellowness (b*). Serum lipid profile of rats was not significantly different. Total serum antioxidant capacity by FRAP was significantly increased only in the ω3‐Q group. Plasma malondialdehyde was similar in the ω3 and ω3‐Q groups, indicating no prooxidative effect of quercetin in vivo. These results suggest that quercetin might be used as a food ingredient in fish gel to improve some nutritional properties of the gel. Copyright © 2005 Society of Chemical Industry