Role of conserved Asn-Tyr-Asp-Tyr sequence in bacterial copper/2,4, 5-trihydroxyphenylalanyl quinone-containing histamine oxidase

Copper amine oxidase contains a covalently bound quinonoid cofactor, 2,4,5-trihydroxyphenylalanyl quinone (TPQ), which is synthesized by post-translational modification of a specific tyrosyl residue occurring in the highly conserved sequence, Asn-Tyr-(Asp/Glu)-Tyr. To elucidate the role(s) of the conserved sequence in the biogenesis of TPQ, each of the corresponding residues at positions 401-404 in the recombinant histamine oxidase from Arthrobacter globiformis has been replaced with other amino acids by site-directed mutagenesis. When Asn-401 was changed to Asp or Gln, the rate of TPQ formation by copper-dependent self-processing was 10(3)- to 10(4)-fold slower than in the wild-type enzyme. When Tyr-402 was replaced by Phe, TPQ was not formed at all, showing that Tyr-402 is essential as the precursor to TPQ. In contrast, Asp-403 could be replaced by Glu without changes in the rate of TPQ formation, whereas its replacement by Asn led to a marked decrease. Furthermore, when Tyr-404 was changed to Phe, TPQ was formed swiftly on incubation with copper ions, but the TPQ enzyme exhibited very low activity with altered substrate specificity. These results collectively indicate that a very rigorous structural motif is required for efficient formation of TPQ and for the catalytic activity in the active site of copper amine oxidases.     

Reduction of loading effect by tungsten etchback in a magneticallyenhanced reactive ion etcher

The plug loading effect occurring during the etchback of tungsten was investigated in a magnetically enhanced reactive ion etcher using SF ₆/Ar mixtures. It was found that while the plug loading effect is independent of varying SF₆/Ar flow rate ratio and magnetic field intensity, it is reduced under the condition of high selectivity of tungsten relative to TiN which was achieved at high chamber pressure and low RF power. It is proposed that when TiN is used as a glue layer, the W etch rate enhancement in the plug is mainly controlled by a local loading effect. Under the optimized etchback conditions the plug loss was successfully controlled without the tungsten residue left on severe topology     

Analysis of culture fluorescence by a fiber-optic sensor inNicotiana tabacum plant cell culture

The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight estimated by the structured kinetic model as well as by empirical correlation.     

Multiresolution segmentation of respiratory electromyographicsignals

Analysis of respiratory electromyographic (EMG) signals in the study of respiratory control requires the detection of burst activity from background (signal segmentation), and focuses upon the determination of onset and cessation points of the burst activity (boundary estimation). The authors describe a new automated multiresolution technique for signal segmentation and boundary estimation. During signal segmentation, a new transitional segment is defined which contains the boundary between background a burst activity. Boundary estimation is then performed within this transitional segment. Boundary candidates are selected and a probability is attributed to each candidate, using an artificial neural network. The final boundary for a given transitional segment is the boundary estimate with the maximum a posteriori probability. This new method has proved accurate when compared to boundaries chosen by two investigators     

Extraction of halide quaternary salts in an organic solvent/water system: Hydrodynamics and mass transfer

The hydrodynamic characteristics and mass transfers of halide quaternary salts between two immiscible phases in a stirred membrane permeation cell were investigated. The concentration of quaternary salt, temperature, solvent and the four kinds of halide quaternary salts were evaluated to achieve the extractive optimum condition. The diffusivity, overall mass‐transfer coefficients and individual mass‐transfer coefficients were determined and correlated in terms of the conventional Sh‐Re‐Sc relationship. The transfer time of quaternary salts across the membrane and the thickness of the hydrodynamic diffusion boundary layer were determined as well, so as to characterize the extractive phenomenon of quaternary salts between the two phases that is useful in phase‐transfer catalysis.     

Strength,toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

The flexural strength and fracture toughness of 30 vol% SiC whisker-reinforced Si₃N₄ material were determined as a function of temperature from 25 to 1400°C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100°C; however, appreciable strength degradation started at 1200°C and reached a maximum at 1400°C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPam^1/2. It was also observed that the composite material exhibited no rising R-curve behaviour at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si₃N₄ matrix did not provide any favourable effects on strength, toughness and R-curve behaviour.     

Non-linear properties of polymer cellular materials with a negative Poisson's ratio

Negative Poisson's ratio polymeric cellular solids (re-entrant foams) were studied to ascertain the optimal processing procedures which give rise to the smallest value of Poisson's ratio. The non-linear stress-strain relationship was determined for both conventional and re-entrant foams; it depended upon the permanent volumetric compression achieved during the processing procedure. Poisson's ratio of re-entrant foam measured as a function of strain was found to have a relative minimum at small strains. The toughness of re-entrant foam increased with permanent volumetric compression, and hence with density.     

Hilar cholangiocarcinoma: thin-section spiral CT findings with cholangiographic correlation

Hilar cholangiocarcinoma, a highly lethal tumor, is difficult to diagnose with conventional computed tomography (CT) because of its small size. Spiral CT allows more effective evaluation of these small lesions and better demonstrates the status of the hepatic arterial or portal venous circulation. Among 27 patients with hilar cholangiocarcinoma (infiltrative in 21, exophytic in two, polypoid in one, diffuse in three), thin-section spiral CT allowed identification of each tumor as an area of focal wall thickening that obliterated the lumen. Seventeen of the infiltrative tumors (81%) showed high attenuation. Identification of the level of biliary obstruction was possible in 63% of the patients (17 of 27). The level of obstruction was underestimated in six patients and overestimated in four. Spiral CT is a valuable method for diagnosis of hilar cholangiocarcinoma; however, spiral CT is less accurate in evaluation of intraductal tumor extent because of the limited z-axis resolution.     

Control of circulating current in two parallel three-phase boost rectifiers

One unique feature in parallel three-phase converters is a potential zero-sequence circulating current. To avoid the circulating current, most present technology uses an isolation approach, such as transformers or separate power supplies. This paper proposes a parallel system where individual converters connect both AC and DC sides directly without additional passive components to reduce size and cost of the overall parallel system. In this case, the control of the circulating current becomes an important objective in the converter design. This paper: (1) develops an averaged model of the parallel converters based on a phase-leg averaging technique; (2) a zero-sequence model is then developed to predict the dynamics of the zero-sequence current; (3) based on the zero-sequence model, this paper introduces a new control variable, which is associated with space-vector modulation; (4) a strong zero-sequence current control loop is designed to suppress the circulating current; and (5) simulation and experimental results validate the developed model and the proposed control scheme.