RF MEMS impedance tuners for 6–24 GHz applications

RF MEMS tuners with wide impedance coverage have been developed for 6–24 GHz noise parameter and load‐pull measurement systems. The tuners are based on triple‐, double‐, and single‐stub topologies loaded with switched MEMS capacitors. Several designs are presented, and they use 10–13 switched MEMS capacitors to produce 1024–8192 (2¹⁰–2¹³) different impedances. The measured impedance coverage agrees well with simulations and it is the widest ever measured impedance coverage from any planar tuner to‐date. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

A thermophilic microbial fuel cell design

Microbial fuel cells (MFCs) are reactors able to generate electricity by capturing electrons from the anaerobic respiratory processes of microorganisms. While the majority of MFCs have been tested at ambient or mesophilic temperatures, thermophilic systems warrant evaluation because of the potential for increased microbial activity rates on the anode. MFC studies at elevated temperatures have been scattered, using designs that are already established, specifically air-cathode single chambers and two-chamber designs. This study was prompted by our previous attempts that showed an increased amount of evaporation in thermophilic MFCs, adding unnecessary technical difficulties and causing excessive maintenance. In this paper, we describe a thermophilic MFC design that prevents evaporation. The design was tested at 57 °C with an anaerobic, thermophilic consortium that respired with glucose to generate a power density of 375 mW m⁻² after 590 h. Polarization and voltage data showed that the design works in the batch mode but the design allows for adoption to continuous operation.     

Reflections in anechoic chambers in 100-200 GHz range

Three anechoic chambers have been tested at 110 and 183 GHz. Typical sidewall reflectivity levels are about -60 dB at 110 GHz and -50 dB at 183 GHz measured with pyramidal horns which have a gain of 20 dB. Backwall reflectivity levels are about -35 dB at 110 GHz and -25 dB at 183 GHz.<>     

A new method for correcting phase errors caused by flexing ofcables in antenna measurements

A simple method for correcting phase errors due to flexing of cables in an antenna measurement setup is introduced. The method that makes it possible to measure the phase error in the cable is described, and the error is removed numerically from the antenna measurement results. The method has been verified with experimental measurements at 10 GHz. The measurements show that the accuracy of the phase correction is limited by the accuracy of the phase measurement device in the system     

Enhanced recovery and purification of Aspergillus glucoamylase from Saccharomyces cerevisiae by the addition of poly(aspartic acid) tails

Poly(aspartic acid) tails of different lengths were fused to the glucoamylase (GA) of Aspergillus awamori by genetic engineering techniques. Tails consisting of 5, 7, and 10 aspartate residues were fused to the N-terminus of the full-length mature GA (aa 1-616) downstream from the intact leader peptide to produce fusion proteins designated GAND5, GAND7, and GAND10, respectively. Three fusion proteins with C-terminal tails were also constructed, designated GACD0, GACD5, and GACD10 (0, 5, and 10 aspartate residues, respectively). For the C-terminal fusion proteins, the tails were fused to a catalytically active but truncated form of GA (aa 1-484). All of the charged tails had the general sequence Met-Ala-Aspn-Tyr, where n = 0, 5, 7, or 10. The modified genes were expressed in the yeast Saccharomyces cerevisiae and the proteins secreted into the culture medium. The enzymes were subsequently purified by affinity chromatography. The specific activity of each purified enzyme was found to be comparable to the wild-type enzyme. The C-terminal tails did not interfere with expression, whereas decreased extracellular glucoamylase activities corresponding to increased tail length were found for the N-terminal fusion proteins. Amino-terminal amino acid sequence analysis of the purified GAND proteins confirmed the authenticity of the amino termini of the modified proteins and showed that both the leader peptidase and KEX2 protease cleavages had occurred faithfully. The increased net negative charge of the GAND and GACD proteins was indicated by both nondenaturing PAGE and isoelectric focusing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reflectivity of absorbers in 100-200 GHz range

Different types (pyramidal, convoluted, wedge, flat) of absorber panel made by several manufacturers have been measured at 107 and 183 GHz. These measurements revealed a rapid degradation of the quality of absorbers from 107 to 183 GHz: reflectivity increased nearly 10 dB. The best absorbers have reflectivities below -40 dB at 107 GHz and about -35 dB at 183 GHz.<>     

Atrazine mineralization potential in two wetlands

The fate of atrazine in agricultural soils has been studied extensively but attenuation in wetland systems has received relatively little attention. The purpose of this study was to evaluate the mineralization of atrazine in two wetlands in central Ohio. One was a constructed wetland, which is fed by Olentangy River water from an agricultural catchment area. The other was a natural fen (Cedar Bog) in proximity to atrazine-treated cornfields. Atrazine mineralization potential was measured by 14CO2 evolution from [U-ring-14C]-atrazine in biometers. The constructed wetland showed 70-80% mineralization of atrazine within 1 month. Samples of wetland water that were pre-concentrated 200-fold by centrifugation also mineralized 60-80% of the added atrazine. A high extent of atrazine mineralization (75-81% mineralized) was also associated with concentrated water samples from the Olentangy River that were collected upstream and downstream of the wetland. The highest levels of mineralization were localized to the top 5 cm zone of the wetland sediment, and the activity close to the outflow at the Olentangy wetland was approximately equal to that near the inflow. PCR amplification of DNA extracted from the wetland sediment samples showed no positive signals for the atzA gene (atrazine chlorohydrolase), while Southern blots of the amplified DNA showed positive bands in five of the six Olentangy wetland sediment samples. Amplification with the trzD (cyanuric acid amidohydrolase) primers showed a positive PCR signal for all Olentangy wetland sediment samples. There was little mineralization of atrazine in any of the Cedar Bog samples. DNA extracted from Cedar Bog samples did not yield PCR products, and the corresponding Southern hybridization signals were absent. The data show that sediment microbial communities in the Olentangy wetland mineralize atrazine. The level of activity may be related to the seasonality of atrazine runoff entering the wetland. Comparable activity was not observed in the Cedar Bog, perhaps because it does not directly receive agricultural runoff. Qualitatively, the detection of the genes was associated with measurable mineralization activity which was consistent with the differences between the two study sites.     

Detailed determination of smoke gas contents using a small‐scale controlled equivalence ratio tube furnace method

A series of tests including seven different materials and products have been conducted using a controlled equivalence ratio tube furnace test method. The main objective of the tests was to determine yields of fire‐generated products at defined combustion conditions. The tube furnace test method was set up and run in close agreement with that described in BS 7990:2003. At the time of experimental work the new tube furnace method was in the process of becoming an international standard. It was thus of interest to make an assessment of the capability of the method for determining production yields of important toxic fire products from different types of materials and products. The test series included solid wood, flexible polyurethane (PUR), fire‐retarded rigid PUR, a polyvinyl chloride (PVC) carpet, a high‐performance data cable with fluorine‐containing polymer matrix, a PVC‐based cable sheathing material and fire‐retarded polyethylene cable insulation material. Duplicate tests were generally conducted at both well‐ventilated and vitiated combustion conditions with these materials. The smoke gases produced from the combustion were quantified for inorganic gases by FTIR technique in all tests. A more detailed analysis of the smoke gases was conducted for some of the materials. This extended analysis contained a detailed assessment of organic compounds including, e.g. volatile organic compounds, isocyanates, aldehydes and polycyclic aromatic hydrocarbons. The analysis further included measurement of the size distribution of fire‐generated particles for some of the materials. The quantification of toxic inorganic gases produced by combustion at both well‐ventilated and vitiated conditions was successful regarding repeatability and stability. Typical yields for the two fire stages investigated were determined for a wide range of materials and products. The detailed analysis of organic compounds further corroborated that the new tube furnace method can replicate defined combustion conditions. Copyright © 2007 John Wiley & Sons, Ltd.