Magnetic Characterization of Fischer-Tropsch Catalysts

INGENIERIE+JDAInternational audienceThis paper reviews recent developments in the application of magnetic methods for investigation of Fischer-Tropsch catalysts involving cobalt, iron and nickel. Magnetic characterization provides valuable information about catalyst reduction, sizes of ferromagnetic nanoparticles, chemisorption on ferromagnetics and topochemical reactions which occur with the catalysts during the genesis of the active phase and in the conditions of Fischer-Tropsch synthesis. The capabilities and challenges of the magnetic methods are discussed.Cet article passe en revue les développements récents dans le domaine de la caractérisation des catalyseurs Fischer-Tropsch à base de cobalt, de fer et de nickel par la méthode magnétique. La caractérisation magnétique fournit des informations précieuses sur la réduction du catalyseur, la taille des nanoparticules ferromagnétiques, la chimisorption, ainsi que sur les réactions topo chimiques qui se produisent avec les catalyseurs au cours de la genèse de la phase active et dans des conditions réactionnelles. Les possibilités et les limites de la méthode magnétique sont examinée

Применение двухточечного метода калибровки для тепловизионных матриц фирмы ULIS

The objective of this work is research and modification of the two-point calibration method for long wavelength infrared uncooled microbolometer ULIS' matrices. The ultimate goal is to obtain better thermal image for the end-user, where quality criteria are such characteristics as a visual contrast, ability to distinguish fine details, and noisy image as less as possible.In considering the most common calibration algorithm of infrared uncooled microbolometer matrices we used the study results of other authors in which results and comparative analyses of the most effective algorithms were provided. Based on these investigations, to make modification have been chosen quite effective and at the same time simple computationally two-point calibration method, which is sufficient for most tasks entrusted to thermal imager.Modification of the two-point calibration method involves introducing variable reference voltages, which nominal values depend on the temperature range of the matrix. In the original version of the algorithm a reference voltage was selected for the whole range of possible temperatures of the matrix, which did not guarantee the required level of minimum sensitivity. The results of the algorithm embedded in a real device and experimental results proved the effectiveness of this modification.The known specialized literature describing calibration methods for long wavelength infrared uncooled microbolometer matrices do not mention this type of modification.The method described in this publication can be applied to various practical implementations of the thermal imagers without cover and algorithms, which can improve image quality.The article shows advisability and effectiveness of using the modified two-point calibration method for design of thermal imagers without cover with a wide range of operating temperatures.Приводятся краткий обзор наиболее распространённых на текущее время методов калибровки (двухточечная и многоточечная) и вариант модифицированного алгоритма двухточечной калибровки приборов бесшторкового типа, построенных на основе неохлаждаемых микроболометрических матриц фирмы ULIS (Long Wavelength Infrared uncooled microbolometer). В статье отражены описание процедуры калибровки, получения результатов, кратко описан интерфейс программы, реализованной на языке С и используемой в данной работе, а так же сам прибор, используемый для апробации модифицированного алгоритма. Результаты данной работы могут быть интересны при практической реализации бесшторковых тепловизоров и алгоритмов улучшения качества изображения

Quantum states and linear response in dc and electromagnetic fields for charge current and spin polarization of electrons at Bi/Si interface with giant spin-orbit coupling

An expansion of the nearly free-electron model constructed by Frantzeskakis, Pons and Grioni [Phys. Rev. B {\bf 82}, 085440 (2010)] describing quantum states at Bi/Si(111) interface with giant spin-orbit coupling is developed and applied for the band structure and spin polarization calculation, as well as for the linear response analysis for charge current and induced spin caused by dc field and by electromagnetic radiation. It is found that the large spin-orbit coupling in this system may allow resolving the spin-dependent properties even at room temperature and at realistic collision rate. The geometry of the atomic lattice combined with spin-orbit coupling leads to an anisotropic response both for current and spin components related to the orientation of the external field. The in-plane dc electric field produces only the in-plane components of spin in the sample while both the in-plane and out-of-plane spin components can be excited by normally propagating electromagnetic wave with different polarizations.Comment: 10 pages, 9 figure

A study of the frequency dependent susceptibility of a colloidal suspension of manganese ferrite (MnFe

Measurements of the complex, frequency dependent susceptibility, χ(ω) = χ′ (ω) − i χ′′ (ω) over the frequency range 50 MHz to 15 GHz, of a surfacted ferrofluid comprising MnFe204 ferrite particles in dibutylphthalat (DBP), as a function of a biasing magnetic field are presented. The biasing field was varied over the range 0 to 100 kAm−1, and has enabled average values of anisotropy constant, $\bar{K}$, and anisotropy field $\bar{H}_{\rm A}$ for the sample to be determined. Ferromagnetic resonance was exhibited for all values of the biasing field, covering the range 1.2 to 8.5 GHz, with the χ′ (ω) component of the susceptibility going negative in the GHz region