Nucleophilic attack by oxyanions on a phosphate monoester dianion: the positive effect of a cationic general Acid

The two negative charges on a phosphate monoester RO-PO32- at neutral pH provide a considerable electrostatic barrier toward reactions with nucleophilic reagents with a negative charge on the attacking atom. Electrostatic repulsion disappears when the hydrolysis of an aryl phosphate monoester is catalyzed by a neighboring cationic general acid. The hydrolysis of 8-dimethylammonium-1-phosphate (1) is catalyzed by oxyanions, fluoride anion, and hydroxylamines at similar rates.     

Daily dietary intake of minor and trace elements by upper social groups in Taiwan

Sixteen minor and trace element contents of diet samples from three different social population groups in Taiwan were determined. Samples were prepared using duplicate portion technique by collecting the 15 subjects ate and drank during a 3-day period. Samples were homogenized, freeze-dried, and elemental concentration of minor and trace elements were determined by instrumental neutron activation analysis. Elemental concentrations and daily dietary intake of the elements were compared with those in the other nations, and possible origins were discussed.     

Determination of pre-scission kinetic energy in low energy fission using isotonic charge distribution model

The spectral lines of the 478 keV prompt -ray from^7*Li produced in the¹⁰B(n, )^7*Li reaction were measured for a silicon wafer coated with a thin boron layer using neutron beams. The shapes of the Doppler broadened lines were found to depend greatly on the angle between the measurement axis and the boron layer surface. The angular dependence was interpreted according to whether the energetic^7*Li ions are ejected into air or into the substance in the forward or backward recoil of^7*Li to the -ray detector.     

Determination of environmentally important metal ions by fluorescence quenching in anionic micellar solution

This work describes the effect of a variety of metal ions as quenchers of the fluorescence of naphthalene, in aqueous micellar solutions of sodium dodecyl sulfate (SDS). The quenching by the metal ions can be adequately described by the Stern-Volmer equation and the best signal to noise ratios are obtained with low micellized detergent concentrations. Apparent Stern-Volmer constants decrease in the order: Fe3+ > Cu2+ > Pb2+ > Cr3+ > Ni2+ and directly reflect the relative sensitivity of the method for these ions. Detection limits (defined as three times the standard deviation of the blank for n= 10) for the fluorescence quenching of naphthalene by the metal ions in aqueous micellar SDS are in the range of 1.0 x 10(-6) to 1.0 x 10(-5) mol dm(-3). The proposed fluorescence quenching method shows good repeatibility for a variety of added quencher metal ions, indicating that anionic micelle-enhanced fluorescence quenching by metal ions constitutes an analytical method of rather general application.     

Facile Synthesis and Characterization of 5-[(3-Methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole and Its Potentiometric Sensor Application in a Polyvinyl Chloride Membrane for the Determination of Copper(II)

A novel Schiff base designated as 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole was synthesized and characterized. A polyvinyl chloride-membrane potentiometric copper(II)-selective sensor was prepared by using the synthesized 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole compound. The prepared polyvinyl chloride-membrane copper(II)-selective sensor exhibited very good selectivity and sensitive potentiometric response towards copper(II) ions compared to a wide variety of other cations. The sensor had a fast response time of <5?s, and showed a linear Nerstian behavior to copper(II) ions over a wide concentration range from 1.0?×?10^?5 to 1.0?×?10^?1 mol L^?1 with a slope of 29.2?±?0.7 and correlation coefficient of 0.9998. The prepared polyvinyl chloride-membrane copper(II)-selective sensor was used for 14 weeks without any significant change in its potentiometric response. The potentiometric response of the developed sensor was highly repeatable. Additionally, the developed sensor was used as an indicator electrode for the potentiometric titration of copper(II) ion with ethylenediaminetetraacetic acid. The sensor was also successfully applied to the direct determination of copper(II) ions in tap water, river water, and dam water samples.     

A comparative analysis of machine learning techniques and fuzzy analytic hierarchy process to determine the tacit knowledge criteria

Knowledge management is widely considered as a strategic tool to increase firm performance by enabling the reuse of organizational knowledge. Although many have studied knowledge management in a variety of business settings, the concept of tacit knowledge, especially the individual one, has not been explored in due detail. The objective of this study is to identify and prioritize individual tacit knowledge criteria and to explain their effects on firm performance. In the proposed methodology, first, the most prevalent individual tacit knowledge variables are identified by means of knowledge elicitation and feature selection methods. Then, the extracted variables were prioritized using machine learning methods and fuzzy Analytic Hierarchy Process (AHP). Support vector machine (SVM), logistic regression, and artificial neural networks are used as the first approach, followed by fuzzy AHP as the second approach. Based on the comparative analysis results, SVM (as the best-performed machine-learning technique) and fuzzy AHP methods were identified for the subsequent analysis. The results showed that both SVM and fuzzy AHP determined time efficiency of employees, communication between employees and supervisors, and innovative capability of employees as the most important tacit knowledge criteria. These findings are mostly supported by the extant literature, and collectively shows the synergistic nature of the utilized analytics approaches in determining individual tacit knowledge criteria.

     

Application of different activation analysis techniques for determination of trace elements in human blood

One of the requirements of stable isotope tracer technique is detection of two isotopes of same element. It is preferable to use instrumental techniques in order not to contaminate the samples. Different instrumental nuclear techniques namely neutron activation analysis (NAA), photon activation analysis (IPAA), and prompt gamma ray activation analysis (PGAA) were tried on human blood samples. The techniques were found to be complementary to each other, NAA being the most sensitive of the three. Zinc is choosen for validation work among the three feasible elements (Zn, Cr, Se) for stable isotope tracer technique. As NAA was not sufficient to detect two isotopes of Zn, a radiochemical separation scheme was developed later.     

One-dimensional solidification of pure materials with a time periodically oscillating temperature boundary condition

A finite difference method is used to solve a one-dimensional solidification problem with a periodic boundary condition prescribed at the bottom of the mold of finite thickness. The temperature distributions in the solidified shell and mold, the position of the moving freezing front, and its velocity are evaluated. Analytical results are obtained for the limiting cases and then compared with the numerical predictions to establish the validity of the model and the numerical approach. Interactive effects of the process parameters such as Stefan number of the solidified shell material, the mold thickness, the thermal conductivity and thermal diffusivity between the shell and mold materials on the evolution of the freezing front and its velocity are investigated in detail. The results show that the solidified materials with larger Stefan number grow slower than those with relatively smaller Stefan number. The impact of oscillating mold temperature boundary on the growth of shell thickness is particularly significant at earlier stages of the process and more pronounced for smaller Stefan numbers. Increasing mold thickness or thermal conductivity ratio between the shell and mold materials slows down the evolution of the shell thickness.