Charge neutralization process of mobile species at any distance from the electrode/solution interface. 1. Theory and simulation of concentration and concentration gradients developed during potentiostatic conditions

The theoretical framework of a general model for the simulation of concentration profiles of electroactive and nonelectroactive species, driven by an electrochemical process under potentiostatic conditions, is presented. Based on this analysis, finite differences simulations are performed to calculate the actual profiles under different experimental conditions. Furthermore, the effect of experimental parameters (diffusion coefficients of the ions of the redox couple or the supporting electrolyte, charge of the different species, etc.) on the concentration profiles is also examined. The results obtained when low and high concentrations of supporting electrolyte are compared aid understanding of the effect of the electrolyte on the measurements. The presented model also underlines the role of supporting electrolyte species when nonspecific techniques are employed to measure the concentration changes produced by electroactive species. On the other hand, if a highly specific technique were used to detect changes in the concentration or concentration gradient of a given species, then it would be possible to estimate the respective profiles of the other species. The simulations suggest that techniques measuring concentration gradients are more sensitive to determining concentration changes than those involving a measurable linearly related to concentration.     

Development of a real-time PCR assay for detection and quantification of enterotoxigenic members of Bacillus cereus group in food samples

A highly sensitive real-time PCR (qPCR) procedure, targeting the phosphatidylcholine-specific phospholipase C gene (pc-plc), was developed for specific detection and quantification of strains belonging to Bacillus cereus group. The target region was selected based on the enterotoxigenic profiles of 75 Bacillus strains. The inclusivity and exclusivity of the RTi-PCR assay were assessed with 59 isolates of the B. cereus group, 16 other Bacillus spp., and 4 non-Bacillus strains. The assay was also used to construct calibration curves for different food matrices, and it had a wide quantification range of 6 log units using both serial dilutions of purified DNA and calibrated cell suspensions of B. cereus CECT 148^T. The detection limit for B. cereus in artificially contaminated liquid egg and reconstituted infant formula was about 3 CFU per reaction or 60 CFU/ml of food, with a relative accuracy of 86.27% to 116.12% in artificially contaminated liquid egg. Naturally contaminated food samples were tested for the presence of B. cereus with the standard method, a conventional PCR and the new developed RTi-PCR assay. Results showed that the new developed RTi-PCR assay is very suitable for detection and quantification of strains of B. cereus group in food samples without an enrichment step.     

Conformational transition in syndiotactic PMMA: 6. Mono- and dichlorobenzene

We have studied the thermal behaviour of syndiotactic PMMA in several solvents by viscometry. We have found a conformational change in the temperature range 293–308 K.     

Long transient oscillations in a class of cooperative cellular neural networks

The real‐time processing capabilities of cellular neural networks (CNNs) are inherently related to the fast convergence time of the solutions toward the asymptotically stable equilibrium points. A typical requirement is that the settling time should not exceed a few (or at most 10) cell time constants. This paper introduces a class of completely stable nonsymmetric cooperative CNN rings whose solutions display unexpectedly long transient oscillations for a wide set of initial conditions and for a wide set of interconnection parameters. Numerical simulations show that the oscillations can easily last hundreds of cycles, and thousands of cell time constants, before settling to a steady state, thus possibly impairing their real‐time processing capabilities. Goal of the paper is also to show, by means of laboratory experiments on a discrete component prototype of the CNN ring, that the long oscillation phenomenon is physically robust with respect to the non‐idealities of the circuit implementation. The experiments show some other peculiar features of the long lasting oscillations as the metamorphosis between different periodic behaviors during the transient. Finally, analytic asymptotic estimates on the duration of the transient oscillations are provided. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of single-walled carbon nanotubes on thermal and electrical properties of silicon nitride processed using spark plasma sintering

Si₃N₄ nanocomposites reinforced with 1-, 2-, and 6-vol% single-walled carbon nanotubes (SWNTs) were processed using spark plasma sintering (SPS) in order to control the thermal and electrical properties of the ceramic. Only 2-vol% SWNTs additions were used to decrease the room temperature thermal conductivity by 62% over the monolith and 6-vol% SWNTs was used to transform the insulating ceramic into a metallic electrical conductor (92 S m⁻¹). We found that densification of the nanocomposites was inhibited with increasing SWNT concentration however, the phase transformation from α- to β-Si₃N₄ was not. After SPS, we found evidence of SWNT survival in addition to sintering induced defects detected by monitoring SWNT peak intensity ratios using Raman spectroscopy. Our results show that SWNTs can be used to effectively increase electrical conductivity and lower thermal conductivity of Si₃N₄ due to electrical transport enhancement and thermal scattering of phonons by SWNTs using SPS.     

A Novel Processing Route to Develop a Dense Nanocrystalline Alumina Matrix (<100 nm) Nanocomposite Material

A dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) toughening alumina matrix nanocomposite with a nanocrystalline (<100 nm) matrix grain size has been successfully developed by a novel processing method. A combination of very rapid sintering at a heating rate of 500°C/min and at a sintering temperature as low as 1100°C for 3 min by the spark-plasma-sintering technique and mechanical milling of the starting γ-Al₂O₃ nanopowder via a high-energy ball-milling process can result in a fully dense nanocrystalline alumina matrix ceramic nanocomposite. The grain sizes for the matrix and the toughening phase were 96 and 265 nm, respectively. A great increase in toughness almost 3 times that for pure nanocrystalline alumina has been achieved in the dense nanocomposite. Ferroelastic domain switching without undergoing phase transformation in nanocrystalline t -ZrO₂ is likely as a mechanism for enhanced toughness.     

Blue–Green Emission in Terbium‐Doped Alumina (Tb:Al2O3) Transparent Ceramics

Alumina (Al₂O₃) is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium‐doped single crystal Al₂O₃ was the basis for the first laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition‐metal dopants because RE doping produces greater efficiencies and lower lasing thresholds. RE‐doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al₂O₃ suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE (～10^?3%) in Al₂O₃ in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb³⁺ ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light‐emitting ceramic. Sub‐micrometer alumina and nanometric RE oxide powders are simultaneously densified and reacted using current‐activated, pressure‐assisted densification (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission (～75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb³⁺ emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.     

Renal and vascular actions of equol in the rat

BACKGROUND: The urinary isoflavonoid equol inhibits membrane Na-K-Cl cotransporters at similar concentrations to those at which furosemide inhibits them, but the significance of this action is not known. OBJECTIVE: To investigate the potential salidiuretic and vascular actions of equol in the rat. METHODS: Renal functioning was assessed in vitro in the isolated perfused kidney and in vivo in conscious rats. The vascular contractility of isolated aorta was assessed. RESULTS: In the isolated perfused kidney equol was concentrated 50- to 70-fold in the urinary fluid, it was 3-4 times less potent than furosemide at increasing diuresis, natriuresis and kaliuresis (the difference was due to its higher protein-binding affinity), and it induced a modest but significant increase in glomerular filtration rate. In vivo, orally administered equol was a modest natriuretic agent, about 8-fold less potent than orally administered furosemide (in molar terms). In isolated aortic rings precontracted by administration of phenylephrine, administration of equol relaxed the contracted aorta at 10-fold lower concentrations (concentration for half-maximal activity 58.9 +/- 16 micromol/l, n = 3) than did furosemide (concentration for half-maximal activity 633 +/- 145 micromol/l, n = 3). CONCLUSIONS: Equol is a modest natriuretic and vasorelaxant agent in the rat. Further studies are required in order to investigate the potential natriuretic and perhaps hypotensive actions of dietary equol precursors (daidzein).