Inductively coupled plasma mass spectrometric determination of molybdenum in urine

A method was developed for the determination of molybdenum (Mo) in human urine by direct dilution of the sample in doubly distilled water with 1% HNO3 (v/v) and inductively coupled mass spectrometry (ICP-MS). In and Y were used as internal standards. Since (98)Mo provides a higher sensitivity, it was chosen as the reference isotope. The influence of different factors, such as sample dilution, HNO3 concentration and the stability of the analyte were evaluated. The detection limit (LOD) was assessed at 0.2 microg/L Mo, while the lower limit of quantification (LOQ) was 0.6 microg/L. Recoveries ranged between 97.2 and 100.7% from solutions containing from 10 to 50 microg/L Mo. Linear calibration curves were generated from 2.1 and 52.1 microg/L with coefficients of variation (CV ) ranging from 1.62 to 3.56%. In order to establish reference values (RV) for molybdenum, the procedure presented here was used to determine Mo in the urine of a population group living in Tuscany, Italy.     

Analysis of uranium and isotopic ratio measurement in fish and marine invertebrates from the North Adriatic Sea by inductively coupled plasma mass spectrometry

Uranium analysis in fish, echinoderms and shellfish samples collected in the north part of the Adriatic Sea is presented. The aim of the work was to evaluate uranium concentrations in samples of this kind, and also to investigate possible contamination from depleted uranium (DU) in consequence of the war operations previously conducted in that area. DU contamination was checked by measuring the (235)U/(238)U isotope ratio. The samples were dissolved according to the EPA 3052 procedure, and the determinations were performed by inductively coupled plasma mass spectrometry (ICP-MS), optimized in order to perform isotope ratio measurements with good precision. The method was validated by evaluating the recovery from spiked samples; results in the range 93-107% were obtained. The isotope ratio measurement was evaluated in terms of accuracy and precision by analyzing the certified reference materials IAEA 326 and GBW 07305, and good agreement with the certified values was obtained here also. The concentration of uranium was higher in invertebrate samples than in fish (0.3-2 microg/g of U vs. 0.05-0.1 microg/g, respectively). The isotope ratio measurements for all the samples gave values very similar to the natural ratio, permitting exclusion of the presence of DU.     

Cooperative emission study in ytterbium doped NdVO4

The infrared and visible cooperative emissions of ytterbium ions are studied in Yb-doped NdVO₄ single crystals. The absorption of optical phonons allows the emissions at room temperature when a Nd:YAG laser is used. Low temperature emissions are observed due to the Nd³⁺→Yb³⁺ energy transfer following an argon ion laser excitation of the Nd³⁺ ions. Analysis of the cooperative emission at low doping concentration (1%) indicates that it is generated by distant pair forming Yb³⁺ ions while at high doping concentration (≥ 5%) close ions magnetically coupled and superexchange mechanisms prevail in the emitting process.     

A branch-and-price algorithm for the multi-depot heterogeneous-fleet pickup and delivery problem with soft time windows

The growing cost of transportation and distribution pushes companies, especially small and medium transportation enterprises, to form partnership and to exploit economies of scale. On the other hand, to increase their competitiveness on the market, companies are asked to consider preferences of the customers as well. Therefore, tools for logistics management need to manage collective resources, as many depots and heterogeneous fleets, providing flexible preference handling at the same time. In this paper we tackle a pickup and delivery vehicle routing problem involving such aspects; customers place preferences on visiting time (represented as soft time windows), and their violation is allowed at a price. Our interest in this problem stems from an ongoing industrial project. First we propose an exact branch-and-price algorithm, having as a core advanced dynamic programming techniques. Then we analyze through a computational campaign the impact of soft time windows management on the optimal solution in terms of both routing and overall distribution costs. Our experiments show that our approach can solve instances of real size, and clarify the practical usefulness of soft time windows management.     

Of higgs,unitarity and other questions

On the verge of conclusive checks on the Standard Model by the LHC, we discuss some of the basic assumptions. The reason for this analysis stems from a recent proposal of an electroweak model based on a nonlinearly realized gauge group SU(2) ⊗ U(1), where, in the perturbative approximation, there is no Higgs boson. The model enjoys the Slavnov-Taylor identities and therefore the perturbative unitarity. On the other hand, it is commonly believed that the existence of the Higgs boson is entangled with the property of unitarity, when high energy processes are considered. The argument is based mostly on the Froissart bound and on the equivalence theorem. In this paper we briefly review some of our objections to the validity of such arguments. Some open questions are pointed out, in particular on the limit of zero mass for the vector mesons and on the fate of the longitudinal polarizations.     

Estimation of Jc(B) dependence from self-field alternating current (AC) losses measured on Bi-2223/Ag tapes

Transport AC losses measured in self-field conditions on multifilamentary Bi-2223 tapes are often found to be lower than those calculated within the framework of the critical state model for a bulk wire with elliptical cross section, though generally higher than predicted for a strip. This effect is sometimes ascribed to the non-ideal geometry of the tapes, which does not exactly reproduce either shape. Here we propose an alternative explanation assuming that the critical current density of superconducting material depends on magnetic field. In practice, we analyzed the AC loss curve and deduced different I_c values for the individual data points, using the standard Norris equation for elliptical conductor. This gives the relation between ‘calculated' I_c and the self-field associated to AC transport current, which can be regarded as an alternative way to qualify the dependence of J_c on magnetic field. Important is that this procedure covers the range of fields below the self-field at I_c where the measurement in background DC field can not be used to determine J_c(B).     

Nd3+ → Yb3+ energy transfer in a codoped metaphosphate glass as a model for Yb3+ laser operation around 980 nm

A complete spectroscopic investigation of a metaphosphate glass with composition Pb(PO₃)₂ doped with various amounts of Nd³⁺ and Yb³⁺ (1 up to 10 at.%) is reported. Efficient Nd³⁺ → Yb³⁺ energy transfers occur both radiatively and non-radiatively, the latter being dominant and partly resonant and partly phonon-assisted by phonons of the order of 950 cm⁻¹, which fits well with the reported Raman spectrum of the material. These transfers mainly concern the ⁴F_3/2 → ⁴I_9/2 emission and the ²F_7/2 → ²F_5/2 absorption transitions of the Nd³⁺ and Yb³⁺ ions around 900 nm, respectively. They are analysed both via spectral and temporal data. The results show that about 5% Nd³⁺ and 5% Yb³⁺ ions have to be incorporated to reach energy transfers exceeding about 65%, which is in agreement with data recently reported in the case of a YAl₃(BO₃)₄ crystal. Simulations based on the obtained data show that laser thresholds of a few tens of mW should be easily attainable by operating the materials in a channel waveguide configuration.