A novel CMOS exponential transconductor operating in weak inversion

A novel CMOS exponential transconductor which employs only three NMOS transistors operating in weak inversion, is presented. The main advantage of the proposed circuit is its wide range of exponential behaviour, which reaches up to five decades of current range, and above 10 μA to an input voltage range of 800 mV. The physical realisation is achieved in two forms: in the first one, the circuit is implemented with discrete MOS transistor arrays by CD4007 series; in the second one, the circuit is fully integrated in a 0.5 μm CMOS standard process. Simulated and experimental results of the proposed exponential transconductor are also presented.     

Evaluation of a Denuder-MOUDI-PUF Sampling System to Measure the Size Distribution of Semi-Volatile Polycyclic Aromatic Hydrocarbons in the Atmosphere

This study describes a field comparison conducted between 2 methods employing different MOUDI impactor configurations to evaluate their performance in sampling and measurement of the size distribution of 15 priority pollutant polycyclic aromatic hydrocarbons (PAHs). Samples were collected during 24 h periods approximately every 7th day, beginning at 8:00 AM, in 2 different sites of the Los Angeles Basin. One site was near Central Los Angeles in an area impacted by high vehicular traffic, whereas the other site was located about 60 km downwind of central Los Angeles (receptor site). Particle samples from about 43 m 3 of air were collected using collocated MOUDI impactors and classified in 3 aerodynamic diameter size intervals: 0-0.18 w m (ultrafine mode I), 0.18-2.5 w m (accumulation mode II), and 2.5-10 w m (coarse mode III). One MOUDI operated in the conventional mode, the other with a vapor trapping system that included an XAD-4 coated annular denuder placed upstream of the impactor and a polyurethane foam plug (PUF) placed in series behind the impactor. PAHs were separated and quantified by HPLC with fluorescence detection optimized for the highest sensitivity. The results showed that for both sites, using either sampling system, the size distributions obtained are similar for the less volatile PAHs (log [ p ° L ] h m 3.2), but different for the more volatile PAHs (log [ p ° L ] S m 2.06). In the central Los Angeles site, the largest PAH fraction was found in the 0-0.18 w m (mode I) size range, typical of primary emissions. At the downwind location, the largest fraction was in the 0.18-2.5 w m (mode II) size range, consistent with an "aged" aerosol. At both sites, albeit not statistically significant, the mean regular to denuded MOUDI mass ratios were 33-36% and 11-19% higher, respectively, for the more volatile and the less volatile PAH groups. Sampling with the regular MOUDI configuration is simpler and thus recommended for measurement of the size distribution of PAHs in either group.     

Coatings prepared from waterborne polyurethane dispersions obtained with polycarbonates of 1,6-hexanediol of different molecular weights

Waterborne polyurethane dispersions (PUDs) were synthesized with polycarbonates of 1,6-hexanediol of different molecular weight (500–3000 Da) and their properties, adhesion (Hatch adhesion) and coatings on stainless steel properties (Pencil hardness, Persoz hardness, gloss at 60°, chemical resistance, yellowness index) were characterized. The hatch adhesion of the polyurethane coatings to stainless steel was very good and decreased slightly by increasing the molecular weight of the polycarbonate of 1,6-hexanediol. Both the Pencil and Persoz hardness values of the coatings increased by increasing the hard segments content in the polyurethane, i.e. by decreasing the molecular weight of the polycarbonate of 1,6-hexanediol, whereas the gloss and the yellowness index were lower for the coatings obtained with the polycarbonate of 1,6-hexanediol of molecular weight of 500 Da. Very good chemical resistance against ethanol for all polyurethane coatings on stainless steel plates was obtained but for long time of ethanol in contact with the coating surface the chemical resistance decreased, more markedly for the polyurethane coating obtained with the polycarbonate of 1,6-hexanediol of higher molecular weight. In summary, the segmented structure of the waterborne polyurethane dispersion determined the properties of the polyurethane coatings obtained from them.     

Thermal Degradation of Polyoxymethylene Evaluated with FTIR and Spectrophotometry

Thermooxidative degradation at and beyond processing temperatures of a polyoxymethylene copolymer has been progressively accelerated to carbonisation through oven-storage aging. The quantification of such degradation was carried out through FTIR spectrography and colour spectrophotometry methods. The state of thermo-oxidation was monitored through the FTIR spectra corresponding to the carbonyl aldehyde group (O=CH) and methylene bending (–CH₂), as well as the chromaticity changes experienced on the sample surface. The results showed that the FTIR bands suggested are a reliable indicator during the initial conditions of degradation, however, the spectrophotometry becomes more appropriate method for more aggressive conditions leading to carbonisation.     

Study,Mechanical Characterization and Mathematical Modeling of Compatible SEBS Blends for Industrial Applications in Orthopedics and Childcare

In this work, a system of compatible blends based on two commercial grades of a thermoplastic elastomer, styrene-ethylene/butylene-styrene (SEBS), with extreme Shore A hardness values (5 and 90), was studied in order to obtain a range of different performance blends for orthopedic and childcare applications, where usually liquid silicone rubber is used. Mechanical properties of different blends were obtained, and Equivalent Box Model (EBM) was used for the prediction of the mechanical behavior. The results show good agreement between the theoretical model and experimental data of new blends of SEBS.     

NUMERICAL STUDY OF THE EFFECT OF THE WALL ON THE DISTRIBUTION OF ISOTHERMAL TWO-PHASE FLOW IN THE BED OF A HYDRODESULFURIZATION REACTOR

Numerical simulations of the isothermal two-phase flow distribution in the packed bed of a reactor used for fuel hydrodesulfurization using the commercial software Fluent are reported. As a first step, the heat and mass transfer as well as the chemical reactions are not taken into account. The reactor considered has, above the bed, a distribution tray equipped with chimneys. A Eulerian three-phase model that considers the catalyst particles as a granular static phase was used following the Holub single-slit model for particle fluid interaction to compute the liquid-solid and gas-solid drag coefficients. Physical properties of the fluids are assumed to be constant. In the present study, the tendency of the liquid to move towards the wall of the reactor was studied in a bed 11 m in depth. The simulations predict that there is no suction effect on the flow caused by the wall. As the two-phase flow moves downward through the bed, a slow radial liquid spreading takes place. However, flow distribution is not completely uniform, at least at a distance of 11 m from the inlet.     

COMPARISON OF PREDICTIVE CORRELATIONS FOR THE NORMAL BOILING DENSITY OF NONPOLAR FLUIDS

Seven empirical correlations for the calculation of the normal boiling density of non polar pure fluids are studied for their accuracy and applicability. One of the correlations is specific only for the normal boiling density, five are based on the corresponding states method (these need the critical parameters and acentric factor as inputs), and the other is a new kind of correlation that uses the Lennard-Jones molecular parameters and the acentric factor as input data. As reference, we take the value for the normal boiling density given by the specific correlation functions proposed in the DIPPR project for 252 nonpolar fluids, grouped into 17 families. In view of the results, we recommend the use of the Yamada-Gunn expression because of its simplicity and because other, less simple, models represent no clear improvement over its accuracy. We also recommend the use of the molecular-parameter model because it gives very good results for some families of fluids.     

Chemical Analysis with High Spatial Resolution by Rutherford Backscattering and Raman Confocal Spectroscopies: Surface Hierarchically Structured Glasses

Copper and iron in glasses constitute classical aims of study because of the optical effects that they produce. Structured materials are also interesting due to the incorporated functionalities derived from their spatial organization. Here, CuO and Fe₂O₃ were incorporated into a standard glass, from which glass coatings with different thicknesses were studied. Whereas iron cations dissolved in the glassy matrix, copper cations saturated it and crystallized at the surface, forming a hierarchical microstructure. The surface microstructure consisted of crystallizations of Tenorite (CuO) forming interconnected walls. The walls surrounding areas of glassy matrix gave rise to a cells microstructure. Rutherford Backscattering Spectrometry provided the composition of the samples with high depth resolution, and Raman Confocal Microscopy determined the phases location and their distribution forming the microstructure. The joint information from both techniques allowed high chemical and spatial resolution of the main cations location for the hierarchical surface microstructure.     

Immunolocalization of substance P and NK‐1 receptor in hofbauer cells in human normal placenta

Substance P (SP) after binding to the neurokinin‐1 (NK‐1) receptor regulates many biological functions. Both SP and the NK‐1 receptor are expressed in human normal placenta cells, monocytes, and macrophages. However, to our knowledge, the presence of both SP and the NK‐1 receptor in macrophages of the placenta, the Hofbauer cells, is unknown. We demonstrate by immunohistochemistry in human normal placenta samples the presence of both SP and NK‐1 receptors in the cytoplasm and in the nucleus of Hofbauer cells. The findings suggest a functional role of the SP/NK‐1 receptor system in the physiology and pathophysiology of Hofbauer cells in the human placenta. Microsc. Res. Tech. 76:1310‐1313, 2013. © 2013 Wiley Periodicals, Inc.