Determination of ytterbium in animal faeces by tungsten coil electrothermal atomic absorption spectrometry

A method for ytterbium determination in animal faeces by tungsten coil electrothermal atomic absorption spectrometry (TCAAS) was developed. Faeces were dry-ashed in a muffle furnace, the ashes were treated with hydrochloric acid, and 10 mul of sample solution were delivered into 150-W tungsten coil atomizer. A matrix-matching procedure employing a 66-s heating program proved to be efficient for obtaining accurate results. Characteristic mass and detection limit were 7.1 pg and 0.35 mug g(-1) Yb, respectively. The tungsten coil atomizer lifetime exceeded 300 firings with digested solutions and R.S.D. of measurements was 1.9% after ten consecutive injections of 10.0 mug l(-1) Yb. Accuracy of the proposed method was assessed by employing a graphite furnace atomic absorption spectrometric procedure. Application of the paired t-test did not reveal any significant difference for ytterbium contents determined by both methods at 95% confidence level. It was demonstrated that the proposed procedure can successfully be used for evaluation of kinetic passage rate of feed through digestive tract of animals.     

Effect of kink-rounding barriers on step edge fluctuations

The effect that an additional energy barrier E_kr for step adatoms moving around kinks has on equilibrium step edge fluctuations is explored using scaling arguments and kinetic Monte Carlo simulations. When mass transport is through step edge diffusion, the time correlation function of the step fluctuations behaves as C(t)=A(T)t^1/4. At low temperatures the prefactor A(T) shows Arrhenius behavior with an activation energy (E_det+3?)/4 if E_kr<? and (E_det+E_kr+2?)/4 if E_kr>?, where ? is the kink energy and E_det is the barrier for detachment of a step adatom from a kink. We point out that the assumption of an Einstein relation for step edge diffusion has lead to an incorrect interpretation of step fluctuation experiments, and explain why such a relation does not hold. The theory is applied to experimental results on Pt(1 1 1) and Cu(1 0 0).     

Heavy fermions in transition metals and transition-metal oxides

Heavy-fermion formation in transition metals and transition-metal oxides is reviewed and compared to observations in canonical f-derived heavy-fermion systems. The work focuses on the dynamic susceptibilities which reveal a characteristic temperature and frequency dependence and which can be unambiguously determined via nuclear magnetic resonance and electron-spin resonance measurements as well as via quasielastic neutron-scattering studies. Different routes to heavy-fermion behaviour are discussed, amongst them Kondo systems, frustrated magnets, and electronically correlated systems close to a metal-insulator transition. From a theoretical point of view, utilizing dynamical mean-field theory, we show that dynamic susceptibilities as calculated for the Hubbard model and for the periodic Anderson model look qualitatively rather similar. These different theoretical concepts describe an universal behaviour of the temperature dependent dynamic susceptibility.Received: 15 May 2003, Published online: 9 September 2003PACS: 71.27.+a Strongly correlated electron systems; heavy fermions - 71.30.+h Metal-insulator transitions and other electronic transitions - 76.60.-k Nuclear magnetic resonance and relaxation - 76.30.Kg Rare-earth ions and impurities     

Decay,interference, and chaos

We establish a close quantitative analogy between the excitation and ionization process of highly excited one electron Rydberg states under microwave driving and charge transport across disordered 1D lattices. Our results open a new arena for Anderson localization -- a disorder induced effect -- in a large class of perfectly deterministic, decaying atomic systems.Received: 15 November 2002, Published online: 8 July 2003PACS: 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 05.45.Mt Quantum chaos; semiclassical methods - 72.15.Rn Localization effects (Anderson or weak localization)     

Magnetic resonance on LiCuVO 4

EPR and ⁷Li NMR measurements were performed in the distorted inverse spinel V(LiCu)O₄ down to 1.5 K. Anisotropy effects on magnetic resonance spectra due to the Jahn-Teller distortion of the oxygen octahedra surrounding the copper ions are discussed. The estimation of the spin-spin interactions deduced from the EPR-relaxation rate Δ H reveals a situation comparable to the prototypical one-dimensional S = 1/2 Heisenberg antiferromagnet CuGeO₃. Approaching three-dimensional antiferromagnetic order ( T _N ≈ 2 K) from above, both magnetic relaxation rates, Δ H _EPR and ⁷ (1/ T ₁ ), respectively, exhibit nearly the same critical divergence reminding to the onset of three-dimensional order in two-dimensional layered systems. Received 22 January 2001 and Received in final form 6 May 2001     

Visualization of pigment distributions in paintings using synchrotron K-edge imaging

X-ray radiography plays an important role in the study of artworks and archaeological artifacts. The internal structure of objects provides information on genesis, authenticity, painting technique, material condition and conservation history. Transmission radiography, however, does not provide information on the exact elemental composition of objects and heavy metal layers can shadow or obscure the ones including lighter elements. This paper presents the first application of synchrotron-based K-edge absorption imaging applied to paintings. Using highly monochromatic radiation, K-edge imaging is used to obtain elemental distribution images over large areas. Such elemental maps visualize the distribution of an individual pigment throughout the paint stratigraphy. This provides color information on hidden paint layers, which is of great relevance to art historians and painting conservators. The main advantage is the quick data acquisition time and the sensitivity to elements throughout the entire paint stratigraphy. The examination of a test painting is shown and further instrumental developments are discussed. PACS 07.85.Qe; 07.05.Pj     

Anisotropic exchange interactions in CuTe2O5

Electron paramagnetic resonance (EPR) was used to study CuTe₂O₅ single crystals at frequencies of 9.4 and 160 GHz. Analytic expressions for the second and fourth moments of the EPR line are deduced with inclusion of the difference between the exchange couplings of the copper spin with its different neighbors. From comparing the calculated and measured EPR linewidths, the positions of copper ions with the strongest exchange interactions are identified. The parameters of the anisotropic exchange interaction between copper ions in a pair are found. The parameter of the exchange interaction between magnetically nonequivalent copper centers is determined from the frequency dependence of the EPR linewidth. The directions of the principal axes of the g tensors are established. The data obtained count in favor of a quasi-one-dimensional model of magnetism in CuTe₂O₅.     

Abrupt changes in the temperature dependence of the ESR linewidth of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> MnO<Subscript>3</Subscript> single crystals

The temperature dependence of the ESR linewidth in La_{1 ? x} Ca _x MnO₃ single crystals with various dopant concentrations (x = 0.18, 0.2, 0.22, 0.25, and 0.3) has been studied. An abrupt decrease in the ESR linewidth has been observed in the samples with a dopant concentration of x = 0.18 and 0.2 near the respective temperatures T _OO′ ≈ 260 and 240 K of the orthorhombic to pseudocubic structural phase transition. The abrupt decrease in the ESR linewidth by approximately 180 Oe has been also observed in the whole temperature range when the concentration is increased from x = 0.2 to x = 0.22. The formula for the fourth moment of the ESR line has been derived including both crystal fields and isotropic exchange interactions and taking into account the difference between the exchange coupling of a spin to its nearest in-plane and out-of-plane neighbors. The formula has been used to estimate the parameter D of the crystalline field on Mn³⁺ ions.     

Orbital freezing and orbital glass state in FeCr2S4

Low-temperature specific heat measurements and dielectric spectroscopy have been performed on polycrystalline and single-crystalline FeCr2S4, the single crystals showing a transition into a low-temperature orbital glass phase. The freezing of the orbital moments is revealed by a glasslike specific heat anomaly and by a clear relaxational behavior of the dielectric permittivity, exhibiting several hallmark features of glassy dynamics. The orbital relaxation dynamics continuously slows down over six decades in time, before at the lowest temperatures the glass transition becomes suppressed by quantum tunneling.     

Magnetization and specific heat of the dimer system CuTe<Subscript>2</Subscript>O<Subscript>5</Subscript>

We report on magnetization and specific heat measurements on single-crystalline CuTe₂O₅. The experimental data are directly compared to theoretical results for two different spin structures, namely an alternating spin-chain and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B 77, 224437 (2008)]. While the analysis of the specific heat does not allow to distinguish between the two models, the magnetization data is in good agreement with the 2D coupled dimer model.