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A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l−1 level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h−1, the enhancement factor was 155, the detection limit was 0.02 μg l−1, the relative standard deviation was 3.2% at 2.0 μg l−1 Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l−1. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples. 相似文献
3.
Alexandros Tzachristas Marilena E. Dasenaki Reza Aalizadeh Nikolaos S. Thomaidis Charalampos Proestos 《Molecules (Basel, Switzerland)》2021,26(10)
Wine metabolomics constitutes a powerful discipline towards wine authenticity assessment through the simultaneous exploration of multiple classes of compounds in the wine matrix. Over the last decades, wines from autochthonous Greek grape varieties have become increasingly popular among wine connoisseurs, attracting great interest for their authentication and chemical characterization. In this work, 46 red wine samples from Agiorgitiko and Xinomavro grape varieties were collected from wineries in two important winemaking regions of Greece during two consecutive vintages and analyzed using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QToF-MS). A targeted metabolomics methodology was developed, including the determination and quantification of 28 phenolic compounds from different classes (hydroxycinnamic acids, hydroxybenzoic acids, stilbenes and flavonoids). Moreover, 86 compounds were detected and tentatively identified via a robust suspect screening workflow using an in-house database of 420 wine related compounds. Supervised chemometric techniques were employed to build an accurate and robust model to discriminate between two varieties. 相似文献
4.
We present a calculation of the differential two-jet cross section in e(+)e(-) annihilation through next-to-next-to-leading order (NNLO) in the strong coupling constant alpha(s). The calculation is performed using a new method for dealing with real radiation suggested recently by us. For the first time, the two-jet event rate is computed directly, without any reference to the inclusive cross section e(+)e(-)-->hadrons. We also calculate the energy distribution of the leading jet in e(+)e(-)-->2 jets and find significant modifications of the shape of this distribution at NNLO. 相似文献
5.
We compute the rapidity distribution of the virtual photon produced in the Drell-Yan process through next-to-next-to-leading order in perturbative QCD. We introduce a powerful new method for calculating differential distributions in hard scattering processes. This method is based upon a generalization of the optical theorem; it allows the integration-by-parts technology developed for multiloop diagrams to be applied to noninclusive phase-space integrals, and permits a high degree of automation. We apply our results to the analysis of fixed-target experiments. 相似文献
6.
It is shown that every properly embedded incompressible surface in a handlebody can be constructed by a canonical gluing process. A simple condition is given which asserts that the result of the gluing process is an incompressible surface. A new notion of isotopy is introduced in order to distinguish surfaces belonging to distinct isotopy classes. Several examples (known and new) are constructed. 相似文献
7.
The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate
in the flat Universe. Modern particle theories provide viable cold dark matter candidates with masses in the GeV-TeV region.
All such candidates will be called WIMPs (Weakly Interacting Massive Particles). The nature of dark matter can only be unraveled
by its direct detection in the laboratory. In this work we present some theoretical elements relevant to the direct dark matter
detection experiments, paying particular attention to directional experiments, i.e. experiments in which not only the energy
but the direction of the recoiling nucleus is observed. Since the direction of observation is fixed with respect to the Earth,
while the Earth is rotating around its axis, in a directional experiment the angle between the direction of observation and
the Sun’s direction of motion will change during the day. So, since the event rates sensitively depend on this angle, the
observed signal in such experiments will exhibit very interesting and characteristic periodic diurnal variation. 相似文献
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Marina A. Medvedeva Theodore E. Simos Charalampos Tsitouras 《Mathematical Methods in the Applied Sciences》2020,43(4):1582-1589
Implicit Runge-Kutta (RK) methods are in common use when addressing stiff initial value problems (IVP). They usually share the property of A-stability that is of crucial importance in solving the latter type of IVP. Radau IIA family of implicit RK methods is among the preferred ones. Especially its fifth-order representative named RADAU5 has received a lot of attention for use with lax accuracies. Here, we try the lesser possible perturbation of its coefficients. Then, we derive a trigonometric fitted modification that is intended to be applied in periodic IVPs. Numerical tests over a variety of problems with oscillatory solutions justify our effort. 相似文献