Processing Aluminum Nitride-Silicon Carbide Composites via Polymer Infiltration and Pyrolysis of Polymethylsilane, a Precursor to Stoichiometric Silicon Carbide

AlN-SiC-particle-reinforced composites have been prepared at lessthan equal to1400°C using submicrometer AlN, -325 mesh alpha-SiC particles, and polymethylsilane (PMS; -(CH₃SiH) _n -) via a polymer infiltration and pyrolysis (PIP) process. PMS is an organometallic SiC polymer precursor that can be modified with 16 wt% cross-linking aid to provide mPMS. mPMS converts to nanocrystalline β-SiC with >80% ceramic yield (1000°C in argon) with some excess (<5 wt%) graphitic carbon. mPMS has been used successfully as a nonfugitive binder for AlN-SiC compacts. Densities of 2.5 versus 2.1 g/cm³ have been obtained after nine PIP cycles for disk-shaped compacts formulated with and without mPMS binder, respectively. alpha-SiC seeds crystallization of β-SiC derived from mPMS at temperatures as low as 1000°C. Some evidence suggests that AlN-SiC solid solutions form at particle/matrix interfaces.     

Synergy effect in the photocatalytic degradation of phenol on a suspended mixture of titania and activated carbon

The photocatalytic degradation of phenol, chosen as an aromatic model molecule, has been performed at room temperature (20°C) in contact with a suspended mixture of titania and of activated carbon (AC). Non-additive adsorption capacities were observed when the solids were mixed, and this was ascribed to a strong interaction, involving half of the surface of titania and ca. 14% of that of AC. A synergy effect was observed with an increase of the first order rate constant by a factor of 2.5. As for neat titania, the same main intermediate products (hydroquinone and benzoquinone) were found but in much smaller quantities and during a much smaller lifetime, suggesting that the same reaction mechanism occurred in the presence of photoinactive AC. The synergy effect was ascribed to an extended adsorption of phenol on AC followed by a transfer to titania where it is photocatalytically degraded. The synergy effect could not be improved by previous physical treatments of the solid mixture such as grinding and sonication. Some phenol remained adsorbed on AC when no traces of organic compounds were detected in the purified water. This adsorbed phenol could be destroyed by illuminated titania while maintaining UV-irradiation. This combined photocatalytic system may appear as a new performing one, more efficient with a shorter time necessary for decontaminating diluted used waters.     

Ropy slime-producing lactic acid bacteria contamination at meat processing plants.

At three Finnish meat processing plants the processing rooms, meat trimmings and carcasses were examined for the presence of ropy slime-producing lactic acid bacteria. Bacterial isolates similar to ropy slime-producing lactobacilli strains able to produce ropy slime on meat products, were recovered from the processing rooms and meat trimmings, indicating that these rooms and raw materials are a source of contamination for ropy bacteria. The ability to produce ropy slime would appear to be a common characteristic of lactobacilli, since altogether 10 different ropy lactobacilli groups were isolated in this study.     

Kinetics and mass transfer effects in the oxidation of ferrous sulfate over doped active carbon catalysts

Ferric sulfate is used in water purification. The oxidation of ferrous sulfate, FeSO₄, to ferric sulfate in acidic aqueous solutions of H₂SO₄ over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and two kinds of catalysts were utilized: active carbon, doped active carbon. Both active carbon and doped active carbon catalysts enhanced the oxidation rate considerably.

Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60–100°C and 4–10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe²⁺ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe²⁺ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe²⁺ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe²⁺ over pure active carbon and doped active carbon catalysts.     

Variability in oil content and fatty acid composition in wild northern currants

Seed oils of wild berries of alpine currant (AC) and northern redcurrant (NRC) were investigated. Oil contents of AC and NRC varied between 4.9 % and 9.7% and between 12.8% and 38.5%, respectively. The proportions of α-linolenic, γ-linolenic and stearidonic acids were higher in NRC (means of 21.7, 12.3 and 5.4%, respectively) than in AC (16.8, 8.6 and 3.0%). The growth areas of NRC can be divided into two distinct groups according to the proportions of different polyunsaturated fatty acids. Oil content of NRC correlated negatively to the proportion of linoleic acid and positively to that of stearidonic acid. There were significant correlations between all polyunsaturated fatty acids in NRC but correlations were less obvious in AC. Interestingly, the correlation between linoleic and γ-linolenic acids was positive in NRC but negative in AC. α-Linolenic and stearidonic acids showed positive correlations in both species. In NRC the synthesis of triunsaturated fatty acids is directed either towards α-linolenic or γ-linolenic acids. Results showed great potential in NRC and AC for plant breeding due to the natural variation in the content and composition of the seed oils for functional nutrients. Received: 20 August 1999 / Revised version: 29 October 1999     

C4NP-无铅倒装晶片焊凸形成生产工艺与可靠性数据

受控倒塌芯片连接新工艺是一种由IBM公司开发、由Suss Micro Tec公司推向商品化的新型焊凸形成技术。受控倒塌芯片连接新工艺采用各种无铅焊料合金致力于解决现有的凸台。形成技术限定,使低成本小节距焊凸形成成为可能。受控倒塌芯片连接新工艺是一种焊球转移技术,熔焊料被注入预先制成并可重复使用的玻璃模板(模具)。这种注满焊料的模具在焊料转入圆片之前先经过检查以确保高成品率。注满焊料的模具与圆片达到精确的接近后以与液态熔剂复杂性无关的简单工序转移在整个300mm(或300mm以下)圆片上。受控倒塌芯片连接新工艺技术能够在焊膏印刷中实现小节距凸台形成的同时提供相同合金选择的适应性。这种简单的受控倒塌芯片连接新工艺使低成本、高成品率以及快速封装周期的解决方法对于细节距FCiP以及WLCSP凸台形成均能适用。     

The Determination of relative amounts of Phases in Binary Mixtures with Quantitative X-Ray Diffraction

The quantitative x-ray diffraction analysis offers often an exact and practical technique to determine the relative amounts of the phases of the solid in question. The sample may contain only one amorphous phase.

The purpose of this paper is to estimate the suitability of this technique to quantify the phase fractions of pharmaceutical substances. Three different method were used to determine the relative amounts of phases. Methods were compared and the major sources of error were estimated. The measurements and calculations are carried out using selegilin hydrochloride, mannitol and modified starch as an example. The results show that the amount of about 2 % of selegilin hydrochloride can be observed reliably from among the mannitol (crystalline substance) or modified starch (amorphous substance). During the work it became obvious that the accuracy of these calculations can essentially be improved planning the measurements carefully.     

Baseband Digital Predistorter with Quadrature Error Correction

In this article simulation and measurement results of a FPGA implementation of a baseband digital complex gain predistorter with a quadrature modulator and demodulation error correction circuits are presented. Four different methods for finding the quadrature error correction values are compared and the effect of quadrature errors to predistortion is discussed. A 50 dB three stage power amplifier chain with an analog quadrature modulator and demodulator was used in the measurements as the device to be predistorted. The signal used in the measurements and simulations was a 30 dBm 18 kHz 16-QAM signal at 400 MHz carrier frequency. In the measurements 15 dB reduction in 3rd order nonlinearity was achieved. The usage of quadrature error correction reduced the adjacent channel power by 9 dB. Ilari Teikari was born in Tampere, Finland, in 1978. He received the M.Sc. (tech.) degree from Helsinki University of Technology (HUT), Helsinki, Finland, in 2002. He is currently working toward D.Sc. (tech) degree in the electronic circuit design laboratory, HUT. His current research intrests are in the area of power amplifier linearization methods and digital circuit design. Jouko Vankka was born in Helsinki, Finland, in 1965. He received the M.S. and Ph.D. degrees in electrical engineering from Helsinki University of Technology (HUT) in 1991 and 2000, respectively. Since 1995, he has been with the Electronic Circuit Design Laboratory, HUT. His research interests include VLSI architectures and mixed-signal integrated circuits for communication applications. Kari A. I. Halonen was born in Helsinki, Finland, on May 23, 1958. He received the M.Sc. degree in electrical engineering from Helsinki University of Technology, Finland, in 1982, and the Ph.D. degree in electrical engineering from the Katholieke Universiteit Leuven, in Heverlee, Belgium, in 1987. From 1982 to 1984 he was employed as assistant at Helsinki University of Technology and as research assistant at the Technical Research Center of Finland. From 1984 to 1987 he was a research assistant at the E.S.A.T. Laboratory of the Katholieke Universiteit Leuven, enjoying also a temporary grant of the Academy of Finland. Since 1988 he has been with the Electronic Circuit Design Laboratory, Helsinki University of Technology, as senior assistant (1988–1990), and the director of the Integrated Circuit Design Unit of the Microelectronics Center (1990–1993). He was on leave of absence the academic year 1992–1993, acting as R&D manager in Fincitec Inc., Finland. From 1993 to 1996 he has been an associate professor, and since 1997 a full professor at the Faculty of Electrical Engineering and Telecommunications, Helsinki University of Technology. He became the Head of Electronic Circuit Design Laboratory year 1998. From 1997 to 1999 he was an associate editor of IEEE Transactions on Circuits and Systems I. He has been a guest editor for IEEE Journal of Solid-State Circuits and the Technical Program Committee Chairman for European Solid-State Circuits Conference year 2000. He has been awarded the Beatrice Winner Award in ISSCC'02 Conference year 2002. He specializes in CMOS and BiCMOS analog integrated circuits, particularly for telecommunication applications. He is author or co-author over a hundred and fifty international and national conference and journal publications on analog integrated circuits. He has several patents on analog integrated circuits.     

Preceramic Polymer Route to Amorphous and Crystalline Potassium Aluminosilicate Powders and Their Electrorheological Properties

The oxide one-pot synthesis (OOPS) process was used to synthesize a polymer precursor to potassium aluminosilicate, KAlSiO₄ (KASp). A KAlSiO₄ gel (KASg) also was produced via a solgel route using the same precursor. The two routes to KAlSiO₄ were explored to compare the effects of the two processing methods on powder properties. The KASp and KASg powders both transformed on heating (.500°C) to amorphous, high-surface-area powders with narrow pore-size distributions (4–24 nm). These anhydrous, amorphous powders were intrinsic electrorheological (ER) materials. Both materials crystallized at } 1070°C, and thermogravimetric analysis, differential thermal analysis, and X-ray diffractometry suggested that they were identical. Diffuse reflectance infrared Fourier transform spectroscopy and scanning electron microscopy proved that the KASp powders were homogeneous, whereas the KASg powders were heterogeneous and segregated. The KASg powders exhibited better ER properties that were associated with the segregated phases.