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101.
Adriaan M. H. van der Veen Milena Horvat Radmila Milačič Tinkara Bučar Urška Repinc Janez Ščančar Radojko Jaćimović 《Accreditation and quality assurance》2001,6(6):264-268
A proficiency test (PT) was carried out to investigate the quality of laboratory results measuring trace elements in sewage sludge. The scheme relied on reference values, established through flame atomic absorption spectroscopy and instrumental neutron activation analysis. Within the framework of the project, ”Proficiency testing in Central and Eastern European Countries”, the measurements were done in parallel using induced coupled plasma mass spectrometry. This paper discusses the design of the PTS, the metrological concepts behind it and the way in which it was operated. The discussion includes the estimation of measurement uncertainty of the reference values obtained, homogeneity testing and its uncertainty evaluation, as well as all relevant quality assurance aspects. From the results, it can be concluded that all measurement methods involved agree within their respective uncertainties. Furthermore, it can be concluded that it is feasible to operate a proficiency test of trace elements in sewage sludge using reference values. The agreement between the reference values and the consensus values is satisfactory. 相似文献
102.
We continue investigations of ?ech closure spaces and their hyperspaces started in [M. Mrševi?, M. Jeli?, Selection principles and hyperspace topologies in closure spaces, J. Korean Math. Soc. 43 (2006) 1099-1114] and [M. Mrševi?, M. Jeli?, Selection principles, γ-sets and αi-properties in ?ech closure spaces, Topology Appl., in press], focusing on generalized upper and lower Vietoris topologies. 相似文献
103.
T.?A.?GloorEmail author F.?Mila 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,38(1):9-12
We calculate the change in the correlation gap of armchair carbon nanotubes with uniaxial elastic strain. We predict that such a stretching will enlarge the correlation gap for all carbon nanotubes by a change that could be as large as several meV per percent of applied strain, in contrast with pure band structure calculations where no change for armchair carbon nanotubes is predicted. The correlation effects are considered within a self-consistent Hartree-Fock approximation to the Hubbard model with on-site repulsion only.Received: 29 December 2003, Published online: 20 April 2004PACS:
62.25. + g Mechanical properties of nanoscale materials - 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.) - 71.20.Tx Fullerenes and related materials; intercalation compounds 相似文献
104.
Ternes M Weber C Pivetta M Patthey F Pelz JP Giamarchi T Mila F Schneider WD 《Physical review letters》2004,93(14):146805
Low temperature (3.9 K) scanning-tunneling spectroscopy on a hexagonal superlattice of Ce adatoms on Ag(111) reveals site-dependent characteristic features in differential conductance spectra and in spectroscopic images at atomic-scale spatial resolution. Using a tight-binding model, we relate the overall spectral structures to the scattering of Ag(111) surface-state electrons by the Ce adatoms, the site dependence to the disorder induced by imperfections of the superlattice, and the opening of a gap in the local density of states to the observed stabilization of superlattices with adatom distances in the range of 2.3-3.5 nm. 相似文献
105.
Alet F Jacobsen JL Misguich G Pasquier V Mila F Troyer M 《Physical review letters》2005,94(23):235702
We study a model of close-packed dimers on the square lattice with a nearest neighbor interaction between parallel dimers. This model corresponds to the classical limit of quantum dimer models [D. S. Rokhsar and S. A. Kivelson, Phys. Rev. Lett. 61, 2376 (1988)]. By means of Monte Carlo and transfer matrix calculations, we show that this system undergoes a Kosterlitz-Thouless transition separating a low temperature ordered phase where dimers are aligned in columns from a high temperature critical phase with continuously varying exponents. This is understood by constructing the corresponding Coulomb gas, whose coupling constant is computed numerically. We also discuss doped models and implications on the finite-temperature phase diagram of quantum dimer models. 相似文献
106.
We investigate the thermodynamic properties of a field-induced supersolid phase in a 2D quantum antiferromagnet model. Using quantum Monte Carlo simulations, a very rich phase diagram is mapped out in the temperature-magnetic-field plane, with an extended supersolid region where a diagonal (solid) order coexists with a finite XY spin stiffness (superfluid). The various quantum and thermal transitions out of the supersolid state are characterized. Experimental consequences in the context of field-induced magnetization plateau materials are briefly discussed. 相似文献
107.
Anestis Antoniadis Irène Gijbels Mila Nikolova 《Annals of the Institute of Statistical Mathematics》2011,63(3):585-615
One of the popular method for fitting a regression function is regularization: minimizing an objective function which enforces
a roughness penalty in addition to coherence with the data. This is the case when formulating penalized likelihood regression
for exponential families. Most of the smoothing methods employ quadratic penalties, leading to linear estimates, and are in
general incapable of recovering discontinuities or other important attributes in the regression function. In contrast, non-linear
estimates are generally more accurate. In this paper, we focus on non-parametric penalized likelihood regression methods using
splines and a variety of non-quadratic penalties, pointing out common basic principles. We present an asymptotic analysis of convergence rates that justifies the
approach. We report on a simulation study including comparisons between our method and some existing ones. We illustrate our
approach with an application to Poisson non-parametric regression modeling of frequency counts of reported acquired immune
deficiency syndrome (AIDS) cases in the UK. 相似文献
108.
109.
Using infinite projected entangled-pair states, exact diagonalization, and flavor-wave theory, we show that the SU(4) Heisenberg model undergoes a spontaneous dimerization on the square lattice, in contrast with its SU(2) and SU(3) counterparts, which develop Néel and three-sublattice stripelike long-range order. Since the ground state of a dimer is not a singlet for SU(4) but a 6-dimensional irreducible representation, this leaves the door open for further symmetry breaking. We provide evidence that, unlike in SU(4) ladders, where dimers pair up to form singlet plaquettes, here the SU(4) symmetry is additionally broken, leading to a gapless spectrum in spite of the broken translational symmetry. 相似文献
110.
Tea Zuliani Janez Ščančar Radmila Milačič 《Analytical and bioanalytical chemistry》2013,405(23):7231-7240
In assessing the environmental hazard of Cr(VI) present in soil, exchangeable Cr(VI) is important, since it can be easily washed out from the upper part of the soil into subsurface soil, surface and ground water, and taken up by plants. The aim of this study was to evaluate the degree of species interconversion that may occur during the extraction of exchangeable Cr(VI) from silty-clay soil with phosphate buffer in order to establish an extraction method that would be effective, accurate and with minimal or no species interconversions. The Cr(VI) concentration in soil extracts was determined by speciated isotope dilution inductively coupled plasma mass spectrometry (SID-ICP-MS). The study was performed on soil samples from a field treated with tannery waste for 17 years. Samples were spiked by enriched stable isotopic solutions of 50Cr(VI) and 53Cr(III) that were added to phosphate buffers (0.1 M KH2PO4-K2HPO4 (pH 7.2) and/or 0.1 M K2HPO4 (pH 8)). To optimize extraction, mechanical shaking and/or ultrasound-assisted extraction were compared. The separation and detection of Cr species was performed by high-performance liquid chromatography (HPLC) ICP-MS. When mechanical shaking was applied, 90 % reduction of Cr(VI) was induced by extraction with 0.1 M KH2PO4-K2HPO4, while with 0.1 M K2HPO4 reduction was around 40 %. To shorten the extraction time and the possibility of species interconversions, ultrasound-assisted extraction was further applied only with 0.1 M K2HPO4. For total extraction of exchangeable Cr(VI) with a maximum 10 % reduction of Cr(VI), five consecutive ultrasound-assisted extractions were needed. Figure
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