Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Compact interdigital filters with transmission zeros in LTCC technology

This article presents a simple topology for the implementation of cross‐couplings between nonadjacent resonators in interdigital stripline filters. This topology affords the inclusion of transmission zeros maintaining a cross‐sectional structure similar to that of a stripline. Therefore, the manufacturing cost is very close to an all‐pole prototype. Two design strategies for the coupling structure are discussed: one of them achieving filters with enhanced performance. Both strategies have been assessed implementing prototypes in low‐temperature cofired ceramic (LTCC) technology. The fabricated filters exhibit operating frequencies at 5775 MHz and 8000 MHz with 2.6% and 3.75% pass‐band fractional bandwidths, respectively, and up to 60 dB IL in the rejection band. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:560–570, 2014.     

The effect of Mo on the catalytic and surface properties of Rh-Mo/ZrO2 catalysts

A series of Rh-Mo/ZrO₂ catalysts with fixed Rh and different Mo loadings were prepared and characterized by H₂ chemisorption, XRD, TPR, TEM and XPS. The catalysts were studied in two reactions: the hydrogenation of carbon monoxide and the hydrogenation of toluene. The results suggest that the increase in the Mo content produces a partial coverage of the support and the Rh particles. Moreover, at high Mo coverage, an increase of the MoO₃ layer thickness is produced. After being treated in hydrogen, the molybdenum oxide remains as slightly reduced particles, while Rh is essentially as Rh⁰, with only a small contribution of Rh+ species. The Mo promotes the formation of oxygenates in the CO hydrogenation and it does not affect the activity in the hydrogenation of toluene.     

Correlation between metal oxidation state and catalytic activity: hydrogenation of crotonaldehyde over Rh catalysts

The effects of the rhodium (oxidation) state on the activity and selectivity for the crotonaldehyde hydrogenation reaction over Rh/Al₂O₃ and Rh/SiO₂ catalysts were examined using the techniques of temperature-programmed reduction, hydrogen chemisorption and X-ray absorption near-edge structure (XANES). In the alumina-supported system, the active phase-support interaction is shown to affect the chemical behavior of rhodium under the influence of a reductive atmosphere by stabilizing Rh³⁺ species. This behavior is not observed (as expected) for Rh/SiO₂ catalysts. The structural and electronic bases of the active phase-support interaction and the effect of the latter phenomenon on the hydrogenation of crotonaldehyde are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The composition,active components and bacteriostatic activity of propolis in dietetics

The composition and bacteriostatic activities of fifteen propolis samples from various botanic and geographic origins were determined. Twenty-six phenolic components were identified by high-performance liquid chromatography with array photodiode detector. Acacetin and apigenin were most abundant. Pinocembrin, quercetin, rutin and vanillin were present in lesser quantities. Variance analysis shows significant differences (P≤0.05) in the contents of phenols, flavonoids and active components. The minimum inhibitory concentration of propolis is about 53 times higher than that reported for tetracycline againstBacillus subtilis andStaphylococcus aureus, and about 400 times higher againstEscherichia coli.     

Formula approximation for flat and hierarchical symbolic analysis

This paper addresses the topic of reducing the complexity of formulae resulting from the symbolic analysis of analog integrated circuits, covering both flat and hierarchical symbolic analysis approaches. Previously reported criteria for flat analysis are first briefly reviewed and their limitations illustrated via examples of practical analog circuits. In all of these criteria simplifications are performed by estimating the numerical values of the symbolic terms at a single point of the parameter space, corresponding to the expected typical values for symbols. Consequent quantitative as well as qualitative inaccuracies resulting from this approach are identified. A new simplification strategy for flat symbolic approaches is then presented in which insignificant terms are deleted taking into account expected ranges of variation in the symbol values. Examples are used to show that this new criterion overcomes the drawbacks encountered in previous ones. Finally, an algorithm to simplify hierarchical formulae is presented which includes consideration of the potential ranges of variation in the symbolic parameter values. This algorithm is also applied to practical analog integrated circuits.1. Most of the results in this paper have been obtained with a 4-Mips and 8-Mbyte physical memory SUN3/260 workstation.2. In the rest of the paper the concept offormula complexity denotes the number of symbolic terms contained in a formula. Each addend in (4) is considered as a term to this purpose.3. For instance, simplification of the voltage gain for the folded cascode OTA of figure 1b, with a maximum error margin of 60% ( _M = 0.6), yields a dc gain deviation of 1.6% [9].4. An analog schematic is said to be sized when a numerical value has been assigned to each circuit element and model parameter.5. In practice a sufficiently fine grid should be defined inside that region.6. Here, symbol is generally applied, in the sense that it may either denote a parameter space variable, a product of variables, or a sum of products.7. The models used in this example are intended only as an illustration. Hence, they do not include all the issues required for practical transconductance amplifier applications.     

Model reference adaptive control of discrete‐time piecewise linear systems

This article presents a switched model reference adaptive controller for discrete‐time piecewise linear systems. In the spirit of the work by Landau in the late seventies, proof of asymptotic stability of the closed‐loop error system is obtained, recasting its dynamics as a feedback system and showing the feedforward and the feedback paths are both passive. The challenge is that both paths can be piecewise linear. Numerical results show excellent performance of the proposed controller even in the face of sudden variations of the plant parameters. Copyright © 2012 John Wiley & Sons, Ltd.     

Aircraft Classification and Acoustic Impact Estimation Based on Real-Time Take-off Noise Measurements

The acoustic impact of aircraft taking-off is an important subject for monitoring and research. It is very useful to analyze the type or class of aircraft that produces high level noises based on take-off characteristics. This paper presents a new method about aircraft classification and the acoustic impact estimation, in areas near an airport, based on real time noise measurement for each take-off. The noise measurements are made with sampling frequency of 50 ks/s (kilo samples per second) and 24-bit resolution analog-to-digital conversion, during 24 s. The aircraft identification is made through a model of two parallel feed-forward neural network combined with a weighted addition. In order to generate the inputs to the neural networks, the noise signal features were obtained from the auto-regressive model and the 1/12 octave analysis. The aircraft is grouped into categories or classes depending on the installed engine type. This system has 13 aircraft categories and an identification level above 80% in real environments. Noise signals, generated during aircraft take-off are measured in a fixed location on the airport runway end using a linear 4-microphone array. The acoustic impact is presented by means of a noise map for each take-off and displays four layers related to four take-off time intervals. Based on International Organization for Standardization, each time interval is represented by an equivalent point sound source location through the estimation of time-difference-of-arrival of the acoustic wave from aircraft taking-off.