Enhanced reduction of Cr(VI) by direct electric current in a contaminated clay

The probable relation between diffuse double-layer processes and redox reactions that enhance degradation or conversion of contaminants under an applied electric field were examined in a clay medium. Kaolinite clay, precontaminated with hexavalent chromium, was the test soil medium. Analyte, containing ferrous iron, was transported through the kaolinite clay using direct electric current. The Cr(VI) reduction to Cr(III) was followed by measuring the soil redox potential and pH at discrete locations in the clay bed. The post-test distribution of Cr showed significantly more Cr(III) than Cr(VI) at low to slightly acidic pH distribution (2 < pH < 6) in clay. The stoichiometric analyses of measured chromium and iron species concentrations versus the measured redox potentials were compared to Nernst equation predictions of an equivalent aqueous system. An average of +0.37 V shift was measured from the linear Nernstian prediction of cell potential. The applied electric field appeared to provide additional "cathodic current" to drive forth the redox reactions. The redox potential shift was explained by possible overpotential development at the clay-water interfaces due to double-layer polarization under the applied field.     

Magnetotransport study on as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs strained quantum well structures

We report the observation of thermal annealing- and nitrogen-induced effects on electronic transport properties of as-grown and annealed n- and p-type modulation-doped Ga_{1 - x}In_xN_yAs_{1 - y} (x = 0.32, y = 0, 0.009, and 0.012) strained quantum well (QW) structures using magnetotransport measurements. Strong and well-resolved Shubnikov de Haas (SdH) oscillations are observed at magnetic fields as low as 3 T and persist to temperatures as high as 20 K, which are used to determine effective mass, 2D carrier density, and Fermi energy. The analysis of temperature dependence of SdH oscillations revealed that the electron mass enhances with increasing nitrogen content. Furthermore, even the current theory of dilute nitrides does not predict a change in hole effective mass; nitrogen dependency of hole effective mass is found and attributed to both strain- and confinement-induced effects on the valence band. Both electron and hole effective masses are changed after thermal annealing process. Although all samples were doped with the same density, the presence of nitrogen in n-type material gives rise to an enhancement in the 2D electron density compared to the 2D hole density as a result of enhanced effective mass due to the effect of nitrogen on conduction band. Our results reveal that effective mass and 2D carrier density can be tailored by nitrogen composition and thermal annealing-induced effects.

PACS

72.00.00; 72.15.Gd; 72.80.Ey     

Characterization and thermoluminescence behavior of beta irradiated NaBaBO3 phosphor synthesized by combustion method

NaBaBO₃ host material was synthesized using the combustion method. In order to optimize the performance of the material, effects of sintering temperatures varying from 600° to 1000?°C were investigated. The sintering temperature and dwell time were found to have pronounced effects on the pure NaBaBO₃ material. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to confirm the phase formation and examine the surface morphology of the prepared powder material, respectively. TL behavior of NaBaBO₃ was studied at various beta doses. It is seen that the sample exhibits well resolved TL glow peak at a peak temperature about 175?°C and corresponding TL intensity increases with the increasing beta dose. However, TL glow peak slightly shifts to lower temperature with the increasing beta dose level. This is the first TL report of a phosphor with a NaBaBO₃ host. The TL kinetic parameters were estimated by the peak shape (PS) method and CGCD software. TL glow curves of NaBaBO₃ consist of several traps and exhibited second order kinetics. A possible TL mechanism was also discussed using the energy level model. The obtained results can provide valuable knowledge related to the investigation of the intrinsic nature characteristics of NaBaBO₃ in research fields pertaining to dosimetry.     

Progression of color decision making in introductory design education

Color comprises both subjective and objective aspects within its contextual nature. Research on color design tends to explore this seemingly contradictory concerns from theoretical point of view, as well as architectural and design practice. The aim of this study was to observe subjective, intuitive or heuristic and objective, knowledge‐based or analytical attitudes toward color in design education. In the study 84 introductory design students were surveyed progressively to understand their color decision criteria after completion of three 2‐dimensional colored exercises, specific in terms of color education. Students' responses to open‐ended questions were coded according to the 5 categories, under 2 decision making processes derived from the literature; heuristic approach: preferential and symbolic criteria, and analytic reasoning: formal, thematic, and systematic criteria. A distinction between associative and emotional aspects of symbolic criteria was also revealed by the data analysis. The findings showed a shift from heuristic responses to analytic reasoning, as expected. Additionally, it is also investigated that students not only used heuristic approaches but also analytical components (formal and systematic) of color decision making in varying degrees as well, even before any color subjects covered. Thematic color decisions became a major part of the students' design considerations upon completion of color subjects. The observed increase in the number of color criteria interrelated by the students' among almost all categories explicated a complex decision making process particularly in color design and education. These findings were expected to lead to some further understanding in color decision making in design.     

A Comparison of Single- and Multi-Objective Programming Approaches to Problems with Multiple Design Objectives

In this paper, we propose and compare single- and multi-objective programming (MOP) approaches to the language model (LM) adaptation that require the optimization of a number of competing objectives. In LM adaptation, an adapted LM is found so that it is as close as possible to two independently trained LMs. The LM adaptation approach developed in this paper is based on reformulating the training objective of a maximum a posteriori (MAP) method as an MOP problem. We extract the individual at least partially conflicting objective functions, which yields a problem with four objectives for a bigram LM: The first two objectives are concerned with the best fit to the adaptation data while the remaining two objectives are concerned with the best prior information obtained from a general domain corpus. Solving this problem in an iterative manner such that each objective is optimized one after another with constraints on the rest, we obtain a target LM that is a log-linear interpolation of the component LMs. The LM weights are found such that all the (at least partially conflicting) objectives are optimized simultaneously. We compare the performance of the SOP- and MOP-based solutions. Our experimental results demonstrate that the ICO method achieves a better balance among the design objectives. Furthermore, the ICO method gives an improved system performance.     

Anodic behaviour of fulvestrant and its voltammetric determination in pharmaceuticals and human serum on highly boron-doped diamond electrode using differential pulse adsorptive stripping voltammetry

The electrochemical oxidation of fulvestrant was made on highly boron-doped diamond electrode using differential pulse adsorptive stripping voltammetry. The highest current intensities were obtained by applying +1.10 V during 150 s for boron-doped diamond electrode. For boron-doped diamond electrode, linear responses were obtained for the concentrations between 1 × 10⁻⁶ and 8 × 10⁻⁵ M in standard samples and between 1 × 10⁻⁶ and 4 × 10⁻⁵ M in serum samples. The repeatability of the method was 0.55 RSD% for differential pulse adsorptive stripping voltammetry. The analytical values of the method are demonstrated by quantitative determination of fulvestrant in pharmaceutical formulations and human serum, without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances. Selectivity, reproducibility, and accuracy of the developed methods were demonstrated by recovery studies.     

Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.     

Solvent extraction of bacteriocins from model solutions and fermentation broths

A novel method for the extraction and purification of bacteriocins (small peptides with antimicrobial properties) from fermentation broths is described. Model solutions of nisin were prepared from Nisaplin®, a commercial whey‐based powder containing about 2.5% nisin and sold as a food preservative. These model solutions and fermentation broths from a culture of nisin‐producing Lactococcus lactis subsp lactis were cross‐flow filtered and stirred with toluene to obtain a white suspension in the toluene layer, which was back extracted with 10 mmol dm⁻³ HCl. Yields of the order of 90% for a single stage extraction were obtained followed by similar yields on back extraction. Yields dropped with decreasing pH, going through a minimum at pH 2. In larger scale experiments (11 dm³) at pH 6, a gel layer was formed which, on centrifugation and drying, gave a white solid containing about 50% nisin, the remainder being water and salt. Further process development would almost certainly bring this figure closer to the small‐scale value. The phase transfer technique was also applied to solutions containing variacin and carnocin (produced by Micrococcus varians and Carnobacterium piscicola, respectively). The mechanism of bacteriocin extraction probably involves concentration of the peptides, which are surface active, at the interface until their solubility is exceeded and they form reverse submicelles, which aggregate into reverse micelles to give a gel. © 2000 Society of Chemical Industry