Long-term transients in a reactor under forced concentration cycling

In the approach to a cycle-invariant state in the forced feed concentration cycling of the CO oxidation over a NiO catalyst, a very long transient has been observed lasting 80 ks or more. This transient appears to be associated only with CO pretreatment of the catalyst and is not a general phenomenon. The slow convergence to the cycle-invariant state reported in certain modelling calculations in the literature appears to have a different cause.     

Synthesis of 2,7‐Carbazolenevinylene‐Based Copolymers and Characterization of Their Photovoltaic Properties

New electroactive and photoactive conjugated copolymers consisting of alternating 2,7‐carbazole and oligothiophene moieties linked by vinylene groups have been developed. Different oligothiophene units have been introduced to study the relationship between the polymer structure and the electronic properties. The resulting copolymers are characterized by UV‐vis spectroscopy, size‐exclusion chromatography, and thermal and electrochemical analyses. Bulk heterojunction photovoltaic cells from different copolymers and a soluble fullerene derivative, [6,6]‐phenyl‐C₆₁ butyric acid methyl ester, have been fabricated, and promising preliminary results are obtained. For instance, non‐optimized devices using poly(N‐(4‐octyloxyphenyl)‐2,7‐carbazolenevinylene‐alt‐3″,4″‐dihexyl‐2,2′;5′,2″;5″,2″′;5″′,2″″‐quinquethiophenevinylene 1″,1″‐dioxide) as an absorbing and hole‐carrier semiconductor exhibit power conversion efficiency up to 0.8 % under air mass (AM) 1.5 illumination. These features make 2,7‐carbazolenevinylene‐based and related polymers attractive candidates for solar‐cell applications.     

Kinetic model for water/oil absorption of mesquite gum (Prosopis juliflora) and gum arabic (Acacia senegal)

The water and oil uptake of mesquite and arabic gums in powdered form was studied at temperatures of 23, 35 and 45°C. A previously proposed equation to predict osmotic equilibrium was tested using the experimental data with both gums and a good statistical fit was obtained. Mesquite gum showed the highest water and oil absorption at all temperatures studied. Temperature dependence of the reciprocal of the S₁ and WL_∞ were determined using an Arrhenius equation. The activation energy for water and oil absorption for gum arabic was 21.98 and 39.57 kJ mol⁻¹, compared to that of mesquite gum having values of 15.79 and 46.16 kJ mol⁻¹, respectively. A second order kinetic model was obtained for water and oil absorption for both gums.     

Detection of failure sites by focused ion beam and nano-probing in the interconnect of three-dimensional stacked circuit structures

Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination.     

Microstructural and textural characterization of a hot-rolled IF steel

The present paper reports the experimental results on the microstructural and textural characterization of a hot-rolled IF steel. The IF steel was hot-rolled in multiple passes in the austenitic field (1,070 °C) followed by air-cooling. SEM, TEM, and LOM were used to image the microstructure of the material. The global texture was determined by X-ray diffraction (XRD) technique. The mesotexture of selected regions was investigated by electron backscatter diffraction (EBSD). Results show the presence of a diffuse (nearly random) and weak texture in the hot-band that consists of recrystallized polygonal grains and subgrains. The fraction of boundaries with misorientations comprised in the interval 2° ≤ ψ < 15° was found to be lower than 5%. It can be concluded that these low angle boundaries and the presence of subgrains can be associated to the existence of a few areas softened by recovery during or after hot rolling in austenitic field.     

A comparative cerebral blood flow study in a baboon model with acetazolamide provocation: 99mTc-HMPAO vs 123I(IMP)

Pharmacological interactions are important when nuclear medical procedures are applied to patients under drug therapy, or drug provocation. This study compares in baboon models (regional) cerebral blood flow [(r)CBF] results from 99mTc-HMPAO and 123I-iodoamphetamine [123I(IMP)] each with and without acetazolamide, the latter a suggested drug for testing cerebrovascular reserve. Expected differences in cerebral uptake were observed between the two radio-tracers without acetazolamide. The increase in tracer uptake resulting from acetazolamide is significantly enhanced for 123I(IMP), which could have diagnostic implications.     

Background memory area estimation for multidimensional signalprocessing systems

Memory cost is responsible for a large amount of the chip and/or board area of customized video and image processing system realizations. In this paper, we present a novel technique-founded on data-flow analysis which allows one to address the problem of background memory size evaluation for a given nonprocedural algorithm specification, operating on multidimensional signals with affine indexes. Most of the target applications are characterized by a huge number of signals, so a new polyhedral data-flow model operating on groups of scalar signals is proposed. These groups are obtained by a novel analytical partitioning technique, allowing to select a desired granularity, depending on the application complexity. The method incorporates a way to tradeoff memory size with computational and controller complexity     

Improving manufacturing by cost-effective process modeling

Computer-aided engineering tools are routinely used to simulate forging and heat-treatment operations and to perform thermal and stress analyses. This review gives a few examples of the current uses of process modeling tools and outlines some developing capabilities and near-term applications.     

Performance analysis of a COFDM/FM in-band digital audiobroadcasting system

In this paper, we present a performance analysis of a coded orthogonal frequency division multiplexing DAB system that is power multiplexed over a commercial FM station. We model the mobile channel with a time-frequency scattering function. Results show that the performance of the FM demodulator is crucial, since the level of the residual FM signal has a strong influence on the BER performance of the COFDM system. As with other mobile communication systems, the use of interleaving greatly enhances the performances