Diode-laser derivative spectroscopy without lock-in amplifier

A derivative spectroscopy allowing the spectrum to be observed in real time at the analogue oscilloscope is developed. A differentiating amplifier is used instead of a lock-in amplifier to obtain the signal proportional to the derivative of the absorption line profile. This approach allows a region of the spectrum to be rapidly identified and the diode-laser spectrometer to be tuned to the strongest absorption line.     

Effect of sulfate synthesis conditions on characteristics of samples with the nanosized η-TiO2 modification

The nanosized titania modification ??-TiO₂ has been obtained from titanyl sulfate with different starting precursor concentration, under different hydrolysis and coagulation conditions. Characteristics of samples (nanoparticle and crystallite size, specific surface, pore volume) have been determined by scanning electron microscopy, small-angle and wide-angle X-ray diffraction, and nitrogen physical adsorption at ?196°C, and their correlation with the synthesis conditions has been established. Optimal technological regimes ensuring fabrication of samples with a high yield of ??-TiO₂ modification and specified functional characteristics have been found.     

Method of fast expansions for solving nonlinear differential equations

A method is proposed for constructing fast converging Fourier series with the help of a special boundary function M _q . The convergence rate of the series is determined by the order q of M _q , which makes it possible to use a small number of series terms. The general theory of constructing fast expansions is described, the error of the partial sum of a series is estimated, and an example of a non- linear integrodifferential problem is considered. Due to its remarkable properties, the fast expansion method can be effectively used in applications.     

Propagation of discontinuity waves in complex rheological media with viscous properties

The propagation of discontinuity waves of various order in rheological media is examined. It is assumed that the region of discontinuity of values can be represented by an intermediate layer of infinitesimal thickness. By means of this representation, results can be obtained for a rather wide class of continuous media with viscous properties, which generalize Duhem's results. The first integrals of the laws of momentum and energy conservation are obtained, which hold inside the intermediate layer at a shock wave.It is shown that when viscosity elements are introduced in a special way into the rheological model of a continuous medium, discontinuity waves of any order are propagated in the medium, and that at the surface of a strong discontinuity in a heat-conducting medium, the temperature is continuous. Additional conditions for strain discontinuities at the viscosity elements are obtained. For certain inclusions of the viscosity elements into the rheological model discontinuity waves do not propagate; instead there is merely a weak discontinuity surface which acts as an interface between the flow region of the continuous medium and the region in the state of rest. Contact discontinuities can occur in any continuous medium.The possible existence of a geometrical discontinuity surface in a viscous gas was examined first by Duhem [1]. He established that singluar strong-discontinuity surfaces cannot take place in a viscous gas. However, if one assumes that the velocity and temperature are continuous in the passage through a singular surface, only contact discontinuities are possible [2].     

A Room‐Temperature Verwey‐type Transition in Iron Oxide,Fe5O6

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO₂) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe₅O₆ stoichiometry. Near 275 K, Fe₅O₆ undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe?Fe chemical bonds. This unique feature highlights Fe₅O₆ as a promising candidate for the use in innovative applications. We established that the minimal Fe?Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general.