A VOLTAMMETRIC FLAVIN MICROELECTRODE FOR USE IN BIOFILMS

Biofilms used in bioelectrochemical systems are expected to transfer electrons using electron transfer mediators. One mediator type, flavins, which includes flavin mononucleotide, riboflavin, and flavin adenine dinucleotide, has been found to be endogenously produced by Shewanella oneidensis MR-1. However, the presence and concentration of flavins inside a S. oneidensis MR-1 biofilm have never been reported. The goal of this study was to develop a flavin microelectrode capable of measuring flavins inside a living biofilm and apply it to a biofilm which produces flavins. Because flavins are electrochemically active molecules, the flavin microelectrode was based on detection via square-wave voltammetry. The microelectrode consisted of a carbon working electrode with a 10-30 μm tip diameter, a built-in platinum counter electrode, and a Ag/AgCl reference electrode, all enclosed in a glass outer case. The microelectrode was calibrated between 0.1 μM and 10 μM flavins and showed a linear correlation between flavin concentration and peak currents located at -424 mV(Ag/AgCl) on a square-wave voltammogram. We also developed a model to explain the electrochemical mechanism of flavin detection, and to determine the effective surface area of the microelectrode, the standard reduction potential, and the transfer coefficient. We found that the effective surface area of the microelectrode was close to 100 times the projected surface area. The model predicted a standard reduction potential for RF/RFH2 of -419 mV(Ag/AgCl) at 20 °C and a transfer coefficient of 0.45. Lastly, we measured flavin concentration inside a S. oneidensis MR-1 biofilm grown on a glass surface using oxygen as the electron acceptor. The flavin concentration reached 0.7 μM, increasing near the bottom of the biofilm, where no oxygen was present. This shows the possibility that flavins are produced in the anaerobic zone to act as intermediate electron acceptors in the deeper parts of the biofilm, where there is no oxygen.     

Performance of Penman-Monteith FAO56 in a Semiarid Highland Environment

Reliable estimates of evapotranspiration are essential for irrigation and water resources planning and management. Although several methods are available for computing reference evapotranspiration (ETo), the provision of complete and accurate climate data is often a problem. Therefore, weighing lysimeter data from a semiarid highland environment were used to evaluate the performance of six commonly used reference evapotranspiration estimation methods with different data requirements (Penman-Monteith-FAO56, Priestley-Taylor, Radiation-FAO24, Hargreaves, Blaney-Criddle, Class A pan). The lysimeter experiments were conducted at Ankara Research Institute of Rural Services in Turkey, during the April–October cropping seasons of the years 2000–2002. The average ETo for the three seasons, computed from the lysimeter data, was 964 mm. The Penman-Monteith-FAO56 method was also evaluated for cases where relative humidity, wind speed, solar radiation, or all three parameters would be missing. This resulted in a total of 10 different methods. The RMS errors (RMSE) and index of agreement for the daily data and the monthly averages as well as the mean absolute error (MAE) for the seasonal totals were computed to compare these methods. The methods were ranked based on the sum of the ranks for all five evaluation criteria. The Penman-Montheith-FAO56 method with the full data set, with replacement of wind speed, and with replacement of relative humidity took the top three spots, with MAEs for the seasonal totals ranging between 40 and 70 mm. The Hargreaves method came in fourth (MAE 54 mm), followed by the Penman-Montheith-FAO56 method with replacement of all three parameters (MAE 57 mm). The RMSE for the monthly average ETo was 0.43 and 0.50?mm?days?1 for the Penman-Monteith-FAO56 without and with replacement of all three parameters and 0.48?mm?days?1 for Hargreaves. Thus, if only temperature data would be available, the much easier to use Hargreaves method would be preferred above the Penman-Montheith-FAO56 equation with replacement of humidity, radiation, and wind speed data, for this semiarid highland environment.     

Taking value-networks to the cloud services: security services, semantics and service level agreements

Cloud services have become an emerging solution for organizations striving to address today’s need for agility, but little research has addressed transitioning multiple, collaborating organizations to what can be referred to as a “value-network cloud.” We know that organizations adopting cloud services to execute business processes must concomitantly reconfigure their security solutions for their integrated intra- and inter-organizational collaborations. We address the question, “What is needed to make it possible for an entire value-network to take secure, collaborative business process executions to the cloud?” Future value-network cloud solutions will require completely new security approaches that will leverage contracted brokering solutions operating as part of the cloud solution. We view value-network cloud security service provisioning as a bundle decision characterized by a mix of communication patterns relevant to intra- and inter-enterprise collaboration. We propose a cloud service broker model—using semantics and SLA based middleware—to serve as a trusted interface between the enterprise, cloud service providers and other organizations collaborating in a value-network. The approach enables IT governance for value-network cloud services. The architectural requirements adapt design principles for infrastructure management tailored from approaches to how business cartels historically conducted secure business dealings.     

The influence of computer-assisted instruction on students’ conceptual understanding of chemical bonding and attitude toward chemistry: A case for Turkey

In this study, the effect of computer-assisted instruction on conceptual understanding of chemical bonding and attitude toward chemistry was investigated. The study employed a quasi-experimental design involving 11 grade students; 25 in an experimental and 25 in a control group. The Chemical Bonding Achievement Test (CBAT) consisting of 15 two-tier questions and the Chemistry Attitude Scale (CAS) consisting of 25 item were the principal data collection tools used. The CBAT and CAS instruments were administered in the form of a pre-test and post-test. Analyses of scores of the two groups in the post-test were compared and a statistically significant difference was found between groups in favor of experimental group. It also seems students from the experimental group were more successful than the control group students in remediation of alternative conceptions. The results of this study suggest that teaching–learning of topics in chemistry related to chemical bonding can be improved by the use of computer-assisted teaching materials.     

Penetrating Sealants for Concrete Bridge Decks—Selection Procedure

The major parameter controlling the effectiveness of penetrating sealants as a means of protecting concrete bridge deck surface is the depth of penetration. The factors affecting the depth of sealant penetration are identified both through a fundamental approach and with reference to the literature on penetrating sealants, concrete deterioration, durability, and permeability. Penetration properties and the use of silane and siloxane as concrete surface sealers are discussed. The effects of surface cleaning methods and the drying period are discussed. Penetrating sealants are effective if proper surface cleaning and application procedures are employed. However, moisture state within the first 6-mm depth controls the depth of sealant penetration. Thus, the factors that affect the drying period before sealant application are identified. Penetrating sealants selection procedure incorporating available test methods is outlined based on the knowledge gained through the fundamental studies of flow phenomenon and literature.     

Evaluating Enzymatic Productivity—The Missing Link to Enzyme Utility

Kinetic productivity analysis is critical to the characterization of enzyme catalytic performance and capacity. However, productivity analysis has been largely overlooked in the published literature. Less than 0.01% of studies which report on enzyme characterization present productivity analysis, despite the fact that this is the only measurement method that provides a reliable indicator of potential commercial utility. Here, we argue that reporting productivity data involving native, modified, and immobilized enzymes under different reaction conditions will be of immense value in optimizing enzymatic processes, with a view to accelerating biotechnological applications. With the use of examples from wide-ranging studies, we demonstrate that productivity is a measure of critical importance to the translational and commercial use of enzymes and processes that employ them. We conclude the review by suggesting steps to maximize the productivity of enzyme catalyzed reactions.     

SUPERCRITICAL EXTRACTION AND DESULPHURIZATION OF BEYPAZARI LIGNITE BY ETHYL ALCOHOL/NaOH TREATMENT 3. ELECTROCHEMICAL CHARACTERIZATION OF ORGANIC SULPHUR COMPOUNDS

The overall objective, of this study is to develop an electrochemical method, that will be complementary to the existing spectroscopic methods, for the characterization of sulphur compounds in coal extracts. Beypazan lignite was used in this study. Supercritical interaction between coal and ethyl alcohol/NaOH (or Ca(OH₂) ) was carried out using a microreactor of 15 ml capacity. Liquid products obtained were separated by liquid chromatography in a glass column have been determined and these provided a ground for the identification of various sulphur functional groups in coal liquids obtained from supercritical interaction between a lignite and ethyl alcohol/NaOH or ethyl alcohol/Ca(OH) ₂ or ethyl alcohol. Organic sulphur compounds determined by this method were dibenzydisulphide, dibenzothiophene and tiophenol     

A ΣΔ micro accelerometer with 6 µg/√Hz resolution and 130 dB dynamic range

This paper reports the implementation of a low noise, high dynamic-range ΣΔ readout for low cost capacitive Micro-Electro-Mechanical Systems (MEMS) accelerometers. The readout circuit sets the bandwidth of the ΣΔ loop through an extra feedback path, and hence allows the closed loop system to operate with the low noise characteristics similar to a second-order ΣΔ analog-to-digital converter. A thorough noise analysis of the proposed accelerometer shows that the mechanical noise is the most significant source and quantization noise is mostly eliminated. Dynamic range (DR) of the system is improved by minimizing the circuit noise and increasing the full scale range (FSR) by high-voltage pulse feedback. Utilization of these techniques allows the implementation of low cost, low noise, and high DR navigation-grade accelerometers, by eliminating the need for large proof mass, large area MEMS sensors. The proposed system can achieve a minimum of 6.0 µg/√Hz noise floor, 3.2 µg bias instability, and a maximum of 130 dB DR at 1 Hz. A FSR of ±20 g is reported for 6.2 µg/√Hz noise floor. This range can be increased up to ±40 g at the cost of noise performance and DR.