Design of transmission line filters and matching circuits using genetic algorithms

A method for designing microwave filters and impedance matching circuits using transmission lines is presented. Transmission line filters with shunt‐connected open circuit stubs and continuously varying transmission line matching circuits are described in detail. The proposed method is based on genetic algorithms and can effectively be applied to various filter and matching circuit design problems without increasing theoretical and computational complexity. Design examples are provided, and the proposed method is demonstrated to be effective in designing transmission line filters and matching circuits. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Rapid and improved determination of furan in baby foods and infant formulas by headspace GC/MS

Furan is a 5-membered ring compound with high volatility. The U.S. Food and Drug Administration (FDA) has recently published a report on the occurrence of furan in a large number of thermally processed foods. However, the FDA's analytical method, using standard curve addition, is not suitable for high-throughput routine laboratory operations. We developed a rapid and improved method for determination of furan in foods by headspace GC/MS. Quantification was achieved by using an internal standard of d4-furan and an external calibration curve of furan normalized against the internal standard. The incubation temperature for equilibration was set at 60 degrees C to avoid the formation of furan during analysis. The levels of furan in baby foods and infant formulas were determined with this method. Validation data showed good precision and accuracy. The LOD and LOQ were 0.2-0.5 ng/g and 0.5-2 ng/g for various food matrixes, respectively. The level of furan detected was in the range of 1.4 to 90 ng/g in baby foods and in the range of non-detectable to 36 ng/g in infant formulas.     

Charge-carrier injection into pentacene thin film formed on Si(111) probed by STM spectroscopy

The injection of charge carriers into a pentacene thin film formed on a Si substrate was investigated by scanning tunneling microscopy (STM). Tip height versus bias voltage (z-V) spectroscopy reveals the characteristic charge transport properties of the molecular film, i.e., the conductivity and the threshold energy of charge injection. The abrupt descent of the tip into the film owing to the transition of film conductance, which depends on the degree of charge carrier injection, was observed for crystallized pentacene thin films. The lower film conductance at around zero bias voltage is still higher than that of a vacuum. This indicates that the carrier injection barrier between the pentacene and the semiconducting substrate is extremely low. The convergence of the carrier injection endpoints into a narrow range of electric-field intensity implies that the main factor contributing to barrier formation and collapse is not the bias voltage but the electric field.     

Developing Superplastic Ductilities in Ultrafine-Grained Metals

Conventional superplasticity is generally achieved in metals having grain sizes in the range of ∼2 to 5 μm, but processing by equal-channel angular pressing (ECAP) provides the opportunity of introducing exceptional grain refinement and producing materials with ultrafine grain sizes in the submicrometer range. These materials have the potential for exhibiting excellent superplastic properties when tested in tension at elevated temperatures and examples are presented for representative aluminum and magnesium alloys. When these ultrafine-grained materials deform in superplasticity, internal cavities develop as in conventional superplastic alloys. An example is presented for an aluminum-based alloy, and it is shown that the cavity growth processes are also similar to those in conventional alloys. This article is based on a presentation made in the symposium entitled “Ultrafine-Grained Materials: From Basics to Application”, which occurred September 25–27, 2006, in Kloster Irsee, Germany.     

Determination of genotoxic phenylhydrazine agaritine in mushrooms using liquid chromatography-electrospray ionization tandem mass spectrometry

A new method with good sensitivity and specificity for detecting and quantifying genotoxic hydrazines, agaritine and 4-(hydroxymethyl)phenylhydrazine (HMPH), was developed using liquid chromatography-electrospray tandem mass spectrometry (MS). Synthetic agaritine and HMPH were structurally assigned by ¹H-, ¹³C- and two-dimensional nuclear magnetic resonance (NMR) analysis (HMBC and HMQC), high-resolution fast-atom bombardment (HR-FAB) MS and time of flight (TOF) MS. The polar molecule agaritine was separated on an ODS column using 0.01% AcOH-MeOH (99:1, v/v) as an eluent with a simple solid-phase extraction cleanup. There were no interference peaks for any of the mushrooms. Agaricus spp. contained 1247 and 2017 µg g^-1 agaritine. Other species of mushroom had no agaritine. Recoveries of agaritine from spiked mushroom samples were 60.3-114%. Intra-day precision values were 5.5 and 4.2%, and the inter-day precision values were acceptable (15.0 and 23.0%), as agaritine is unstable. The limit of quantification was 0.003 µg g^-1. Even a trace amount of agaritine in mushrooms can, therefore, be determined using this method. We also directly analysed HMPH, an active free hydrazine form of genotoxic agaritine, and obtained direct evidence of its absence from mushrooms. A precursor ion scan confirmed that agaritine derivatives, which could exert similar toxicity, were absent. The results indicate that this specific and sensitive analytical method for detecting and quantifying agaritine and its derivatives could help evaluate the risk of mushroom hydrazines to humans.     

Development of a ligation-based impedimetric DNA sensor for single-nucleotide polymorphism associated with metabolic syndrome

Single-nucleotide polymorphism (SNP) detection is becoming important in molecular diagnostics, clinical assay, and novel drug development. Electrochemical methods are well suited for the DNA diagnostics system. Since electrochemical reactions directly emit an electronic signal, expensive signal transduction equipment is not required. We describe the development of a novel DNA sensor that utilizes impedance spectroscopy and DNA ligation reaction on a gold electrode. Impedance spectroscopy enables label-free detection and is nondestructive and useful in equivalent circuit models for interpretation on an electrode surface, whereas from the ligation reaction, the specificity is derived by the allele-specific oligonucleotide of the capture probe on immobilized gold electrode. In other words, DNA diagnostics system using the combination of impedance spectroscopy and ligation reaction is simple, rapid, and allele specific. In this report, we have described a ligation-based impedimetric DNA sensor and the analysis of Trp64Arg polymorphism in the beta3-adrenergic receptor gene (ADRβ3).     

The congruent melting composition of strontium barium niobate

The congruent melting composition of strontium barium niobate has been investigated over the ternary composition region by DTA, X-ray fluorescence, Curie temperature and lattice parameter measurements. The composition of congruent melt was found to be close tox=0.61,y=0.4993 for the formula (Sr _x Ba_1–x O)_1–y . (Nb₂O₅) _y . Striation-free single crystals are grown from the melt with this composition. The conceivable reasons for the discrepancy between the results of this work and the previous data are briefly discussed.