Complex magnetic differentiation of cobalts in Nax_{x}CoO2_{2} with 22K N\'eel temperature

Single crystals of sodium cobaltates Na$_{x}$CoO$_{2}$ with $x \approx 0.8$ were grown by the floating zone technique. Using electrochemical Na de-intercalation method we reduced the sodium content in the as-grown crystals down to pure phase with 22 K N\'eel temperature and $x \approx 0.77$. The $^{59}$Co NMR study in the paramagnetic state of the $T_{N}=22$ K phase permitted us to evidence that at least 6 Co sites are differentiated. They could be separated by their magnetic behaviour into three types: a single site with cobalt close to non-magnetic Co$^{3+}$, two sites with the most magnetic cobalts in the system, and the remaining three sites displaying an intermediate behaviour. This unusual magnetic differentiation calls for more detailed NMR experiments on our well characterized samples.Comment: 5 pages, 4 figures, submitted to JETP Let

Correlation Effects and Non-Collinear Magnetism in the Doped Hubbard Model

The ground--state magnetic phase diagram is investigated for the two-- and three--dimensional $t$--$t'$ Hubbard model. We take into account commensurate ferro--, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often missed in previous investigations. We trace the influence of correlation effects on the stability of both spiral and collinear magnetic order by comparing the results of employing both the generalized non-correlated mean--field (Hartree--Fock) approximation and generalized slave boson approach by Kotliar and Ruckenstein with correlation effects included. We found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistic large Hubbard $U$, if the correlation effects are taken into account. The electronic phase separation plays an important role in the formation of magnetic states and corresponding regions are wide, especially in the vicinity of half--filling. The details of magnetic ordering for different cubic lattices are discussed.Comment: Invited Report on the Moscow International Symposium on Magnetism MISM-2014, 6 pages, final versio

Atomic Absorption, Theory

The theory of atomic absorption spectroscopy is presented, covering atom production, atomic absorption and emission line shapes, and methods for calibration and for dealing with interferences. © 1999 Elsevier Ltd All rights reserved

Irradiance distribution in the image of a tube electrothermal atomizer

An algorithm is proposed that allows the calculation of irradiance distribution in the image of a three-dimensional emitter formed by an imaging mirror. The approach is based on a rigorous ray-tracing algorithm supplemented with calculation of radiant flux transferred along each ray. Based on the algorithm, a computer program has been developed to model image formation of a tube electrothermal atomizer in a conventional atomic absorption spectrometer. Image formation of an isothermal and non-isothermal furnaces with and without platform has been considered. The effect of the atomizer misalignment on the irradiance distribution in the image has been modeled. © 1997 Elsevier Science B.V

Correlation between analytical signal and rate of sample atomization in electrothermal atomic-absorption spectrometry

The relationship between an analytical signal, recorded at the spectrophotometer output, and the rate of sample atomization in the furnace has been analysed theoretically. The atomic transfer in the gas phase and the time constant of the recording system are shown to cause the broadening, the shift and the decrease in the peak height of the output signal, compared with the atomization pulse. These distortions can cause smoothing in the multiple peak of atomization. A simple criterion of their negligibility has been proposed. A solution of the inverse problem has been obtained, allowing reconstruction of the initial sample atomization rate from the recorded analytical signal. An efficient algorithm allowing the on-line processing of signals in the spectrophotometer microcomputer has been proposed. The distorting influence of transfer processes and of the recording system upon the shape of Arrhenius plots have been analysed. © 1991

Three dimensional modeling of air flow, aerosol distribution and aerosol samplers for unsteady conditions

Despite the importance and wide use of aerosol samplers, their basic characteristics including gas flow dynamics, sampling, and aspiration efficiency are still not fully understood and characterized. This is especially the case when a personal inhalable sampler operates under conditions of calm or slowly moving air. Under such conditions, the results may be affected by the breathing of the person. The development of the next generation of sampling devices should be facilitated by the improved knowledge derived from mathematical studies of particle motion in the complex flows around bluff bodies where aspiration occurs. In this work, a three-dimensional and time dependent model of aerosol sampling is developed that can be applied to any feasible aspiration situation. Direct accounting for all the three spatial coordinates and temporal dependence makes the model four dimensional. In order to investigate aspiration characteristics when a sampler is fixed on a person, a digital model of a person is developed. The "digital mannequin" can breathe through the mouth or nose and is heated to body temperature to account for convection effects of warm air around the body. The developed model allows simulation of nonstationary air flow and aerosol particles dynamics around any bluff body in both indoor and outdoor conditions. The gas flow and aerosol particles dynamics around a breathing person at the conditions of calm or slowly air moving are computed for both mouth and nasal breathing. It is shown that in such a situation the aspiration efficiency is place and time sensitive. Temporal dependences of aspiration efficiency are computed and averaged characteristics are derived. © The Royal Society of Chemistry

Multidimensional integration of absorbances: An approach to absolute analyte detection

The problem of absolute analyte detection is considered in this paper. It is shown that integration in absorbance, not in intensity, is a pre-requisite for absolute detection in atomic absorption spectrometry. A design for an atomic absorption spectrometer of the future is described which measures absorbance resolved in three key areas: wavelength, space and time. Intensity must be measured with sufficient temporal, spatial and spectral resolution to guarantee the accuracy of the computed absorbance. Technically, such measurements can be made simultaneously with a continuum source, a high resolution echelle spectrometer and a two dimensional solid-state array detector. All computed absorbances are fully background and stray light corrected. With such measurements, and a proper optical configuration, absolute analyte detection can become a reality and the possibility of absolute analysis becomes more obtainable