On the stability of a polling system with an adaptive service mechanism

We consider a single-server cyclic polling system with three queues where the server follows an adaptive rule: if it finds one of queues empty in a given cycle, it decides not to visit that queue in the next cycle. In the case of limited service policies, we prove stability and instability results under some conditions which are sufficient but not necessary, in general. Then we discuss open problems with identifying the exact stability region for models with limited service disciplines: we conjecture that a necessary and sufficient condition for the stability may depend on the whole distributions of the primitive sequences, and illustrate that by examples. We conclude the paper with a section on the stability analysis of a polling system with either gated or exhaustive service disciplines.     

Measurement of naturally occurring radioactive materials (NORM) in beach sand minerals using HPGe based gamma-ray spectrometry

This paper discusses the measurement of naturally occurring radioactivity materials (NORM) in beach sand minerals using high resolution gamma spectrometry. In India, the beach sand minerals of economic interest from coastal Kerala, Tamil Nadu and Orissa are enriched with NORM due to the occurrence of monazite deposits and heavy minerals such as zircon, ilmenite, magnetite, garnet, rutile etc. Since many of these ores are rich in ²³²Th and other radio elements, certification of radioactivity levels has become mandatory in recent years. The average activity concentrations of ²²⁶Ra in zircon, rutile and garnet were 3,531, 1,134 and 17 Bq kg^?1, respectively. The average activity concentration of ²³²Th observed in zircon, rutile and garnet were 618, 454 and 64 Bq kg^?1, respectively. Concentration of ²²⁶Ra, ²³²Th, and ⁴⁰K in ilmenite ore ranged from 17.6–444 Bq kg^?1, 80.4–1971 Bq kg^?1 and ≤5.5–25.0 Bq kg^?1, respectively.     

Speciation analysis of chromium in drinking water samples by ion-pair reversed-phase HPLC–ICP-MS: validation of the analytical method and evaluation of the uncertainty budget

The approach presented in this article refers to the modification of a method for the detection and quantitative determination of chromium species in water by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The main aim of this work was to establish a detailed validation of the analytical procedure and an estimation of the budget of measurement uncertainty which was helpful in recognizing the critical points of the presented method. As a result of the method validation experiment, the obtained limit of quantification, repeatability and intermediate precision were satisfied for the quantification Cr(III) and Cr(VI) in water matrices. The trueness of the method was verified via an estimation of the recovery of the spiked real samples. The recovery rate of both determined analytes was found to be between 93 and 115 %. Considering that the validation of the method and the evaluation of measurement uncertainty are crucial for quantitative analysis, the above-mentioned assessment of the uncertainty budget was performed in two different ways: a modelling approach and a single-laboratory validation approach. The measurement uncertainties of the results were found to be 4.4 and 7.8 % for Cr(III), 4.2 and 7.9 % for Cr(VI) using the classical concept and method validation data, respectively. This paper is the first publication to presenting all the steps needed to evaluate the measurement uncertainty for the speciation analysis of chromium species. In summary, the obtained results demonstrate that the method can be applied effectively for its intended use.     

Stereoselectivity and kinetics of [4 + 2] cycloaddition reaction of cyclopentadiene to para‐substituted E‐2‐arylnitroethenes

In spite of diversified electrophilicity of E‐2‐arylnitroethenes, their [4 + 2] cycloaddition reactions with cyclopentadiene leads to the corresponding 6‐endo‐aryl‐5‐exo‐nitronorbornenes and 6‐exo‐aryl‐5‐endo‐nitronorbornenes as the only reaction products. Stereoselectivity, substituent and solvent effects, and activation parameters, suggest that these reactions occur via a synchronous concerted mechanism on both competing pathways. The experimental results obtained are consistent with the data from B3LYP/6‐31G(d) calculations. Due to high electrophilicity of E‐2‐arylnitroethenes, the reactions studied should be considered as polar [4 + 2] cycloadditions. Copyright © 2011 John Wiley & Sons, Ltd.     

A note on the subexponential asymptotics of the stationary distribution of M/G/1 type Markov chains

Masuyama (2011) obtained the subexponential asymptotics of the stationary distribution of an M/G/1 type Markov chain under the assumption related to the periodic structure of G-matrix. In this note, we improve Masuyama’s result by showing that the subexponential asymptotics holds without the assumption related to the periodic structure of G-matrix.     

Simultaneous determination of Cd,Cr, Cu,Ni, Pb and Zn in sewage sludge by slurry introduction ICP-OES method

In order to evaluate the slurry nebulisation method as an alternative method for analysis of sewage sludge, the metal content of sludge samples of different origins was determined. The concentrations of six elements: Cd, Cr, Cu, Ni, Pb, and Zn were determined by introducing the sludge as a slurry into an inductively coupled plasma optical emission spectrometer (ICP-OES). Calibration was performed by using aqueous standard solutions. For comparison, the sewage sludge was also digested by microwave digestion and introduced into the plasma as an aqueous solution. The accuracy of the method was checked by analysing a sewage sludge certified reference material (CRM 007-040 Sewage Sludge). The Student's t-test showed that values obtained using slurry nebulisation were close to the certified values at a 95% confidence level. The values of elements Cd 11.1?±?0.8; Cr 37.7?±?3.3; Cu 563.3?±?38.4; Pb 119.2?±?10.1; Zn 729?±?68.2?mg?kg^?1 obtained using this method were comparable with those obtained using the conventional method. The slurry method can, therefore, be successfully applied to the determination of content of each element in sewage sludge with RSD less than 3%, without the need to predissolve them. This could avoid the use of hazardous chemicals, incomplete dissolution and loss of volatile analytes.     

Two algorithms for the exchange lemma

Numerical Algorithms - In this note, we present two new algorithms for the Steinitz Exchange Lemma. They are grounded on a single application of a procedure (finding either a row echelon form or a...     

High Pressure effect on fluorescence lifetime τ for magnetic dipole 5D0→5F1 transitions in YAG:Eu3+

The fluorescence lifetime for magnetic dipole ⁵D₀→⁷F₁ transition in yttrium aluminum garnet doped with Eu³⁺ (YAG:Eu³⁺) crystal was studied under the pressure of up to 10.4?GPa at room temperature. The fluorescence lifetime τ (⁵D₀→⁷F₁ transition) slowly decreased with pressure. The pressure effect on τ (⁵D₀→⁷F₁ transition) was explained with a model which considered pressure effect on line position: inter-ionic distance, ion volume, molecular volume, ion polarizability, molecular polarizability, sample refractive index, and surrounding hydrostatic medium refractive index. The fluorescence lifetime τ calculated by the presented model was in close correspondence with the experimental values.     

A branch-and-cut method for the obnoxious p-median problem

The obnoxious p-median (OpM) problem is the repulsive counterpart of the ore known attractive p-median problem. Given a set I of cities and a set J of possible locations for obnoxious plants, a p-cardinality subset Q of J is sought, such that the sum of the distances between each city of I and the nearest obnoxious site in Q is maximised. We formulate (OpM) as a {0,1} linear programming problem and propose three families of valid inequalities whose separation problem is polynomial. We describe a branch-and-cut approach based on these inequalities and apply it to a set of instances found in the location literature. The computational results presented show the effectiveness of these inequalities for (OpM). The work of the first author has been partially supported by the Coordinated Project C.A.M.P.O. and that of the third author by a short mobility grant, both of the Italian National Research Council.