DYNAMIC ATOMIC FORCE MICROSCOPY RESOLVED BY WAVELET TRANSFORM

Atomic Force Microscopy (AFM) is perhaps the most significant member of the scanning probe microscopes family and, because of its capability of working in air and liquid environments with virtually no limitations on imaging conditions and types of samples, it is definitely one of the most widely used. It has become an indispensable tool to measure mechanical properties at the nanoscale in various research contexts. Scanning probes used in AFM are micromechanical oscillators (typically cantilevers) and the theory of AFM dynamics is based on the analysis of the oscillating modes of beam resonators or the simpler spring-mass model. Cantilevers can be driven by the thermal excitation and/or an external driver. Usually cantilevers are driven near resonances corresponding to flexural eigenmodes that can be described as damped harmonic oscillators. Advanced techniques consider multifrequency excitation or band excitation to broaden the measurable events in tip-sample interactions, thus expanding the variety of sample properties that can be accessed. Multifrequency methods imply excitation and/or detection of several frequencies of the cantilever oscillations and concern the associated nonlinear cantilever dynamics. Such excitation/detection schemes provide higher resolution and sensitivity to materials properties such as the elastic constants and the sample chemical environment with lateral resolution in the nanometer range. In order to measure these parameters, information on peak force of interaction, energy dissipation and contact dynamics is required. Techniques to measure the parameters of the cantilever in the stationary regime are well established. In dynamics methods the external driver (thermal noise, piezoelectric driver, etc.) excites the cantilever and a number of techniques have been implemented to gain information from the tip-sample interactions, but usually the interaction of the tip with the surface is revealed by the modification of the average value of the amplitude, frequency or phase shift over many oscillation cycles. Reconstruction of the complete evolution of the interaction force between the tip and the sample surface during a single interaction event is not even considered. As an alternative to these well established techniques and to push further the AFM possibilities, it is important to examine the possibility of analyzing single-event or impulsive interactions. This opens the possibility to capture the information conveyed by the sensing tip in a single interaction, in contrast to the cycle average used in many dynamic techniques. The single-event interactions are basically of the impact kind, with the simultaneous excitation of many cantilever eigenmodes and/or harmonics. The averaging techniques provide superior sensibility, allowing to probe the details of force interactions down to the molecular level, but to study single-event interactions it is mandatory to provide analysis techniques that are able to characterize all excited cantilever oscillation modes at once without averaging. The temporal evolution of the amplitude, phase and frequency during few oscillation cycles of the cantilever provides information that cannot be obtained with standard methods. In the present thesis a data analysis method allowing to retrieve these quantities during an impulsive cantilever excitation is proposed. This thesis concentrates on the dynamics of the flexural modes of the thermally driven cantilever in air when its tip is excited by a single impact on the sample surface. The signal analysis is based on the combination of wavelet and Fourier transforms that can be applied to a broad class of AFM impulsive measurements. To exemplify the method, a short time interval around the jump-to-contact (JTC) transition in ambient conditions is investigated, with the aim to characterize the transient excitation of the cantilever eigenmodes before and after the impact. The experimental evidences that high-order flexural modes are excited in air upon a single impact tip\u2013sample interaction induced by the JTC transition are presented. The way to retrieve information about the instantaneous total force act ing on the cantilever tip, contact dynamics and energy dissipation at all frequencies simultaneously, without averaging or interruption, is developed. The exploration of these transient conditions of the cantilever is not possible with dynamic techniques based on the resonant driving or using Fourier transform analysis alone. The analysis presented in this work is useful to deal with nonrepeatable experiments and to determine the exact single interaction dynamics in terms of the full cantilever spectral excitations, features that are not normally considered in dynamical AFM techniques

On the cellular autoimmune mechanism for eliminating erythrocytes normally and under extreme influences

The presence of an autoimmune cellular mechanism for destroying erythrocytes on the basis of results of experiments in vivo is demonstrated in the blood and the organs. This mechanism is made up of a population of immunocompetent killer-lymphocytes which originates in the bone marrow and the thymus, and which is manifested in the local hemolysis effect

Internationalization as a trend of Russian higher education system

Internationalization and globalization processes are the main factors that define the modern evolution of higher education system in Russia and in the world. The article considers advantages and obstacles of internationalization process in Russia, and shows on an example of ETU "LETI", that one of the key components to accelerate the internationalization process could be development and launch of Master's degree programs in English

Multi-frequency data analysis in AFM by wavelet transform

Interacting cantilevers in Atomic Force Microscopy (AFM) experiments generate non-stationary, multi-frequency signals consisting of numerous excited flexural and torsional modes and their harmonics. The analysis of such signals is challenging, requiring special methodological approaches and a powerful mathematical apparatus. The most common approach to the signal analysis is to apply the Fourier transform (FT) analysis, which decomposes the signal into constituent frequencies displayed in the spectrum as resonance peaks. FT analysis gives accurate spectra for stationary signals. For signals changing their spectral content over time, FT provides only an averaged spectrum. Hence, for non-stationary and rapidly varying signals, such as those from interacting AFM cantilevers, a method that shows the spectral evolution in time is needed. One of the most powerful techniques, allowing detailed time-frequency representation of signals, is the wavelet transform (WT). WT is a method of analysis that allows representation of energy associated to the signal at a particular frequency and time, providing correlation between the spectral and temporal features of the signal, unlike FT [1, 2]. This is particularly important in AFM because signals nonlinearities contains valuable information about tip-sample interactions and consequently surfaces properties [3-5]. The present work is aimed to show the advantages of WT in comparison with FT using as an example the force curve analysis in dynamic force spectroscopy

EXTRACTION OF COPPER, COBALT AND NICKEL IONS FROM AQUEOUS SOLUTIONS BY EXTRACTANT CYANEX 272

The extractant CYANEX 272, which active component is di(2,4,4-trimethylpentyl)-phosphinic acid (C8H17)2POOH, is effective for extraction of copper (II), cobalt (II) and nickel (II) ions. The extraction of metal ions using di(2,4,4-trimethylpentyl)-phosphinic acid as an extractant is carried out due to the formation of an organophosphorus complex with wide pH range: copper at pH > 2, cobalt at pH > 3, and nickel at pH > 5. They are extracted with an organic phase: copper at pH = 3-7, cobalt at pH = 4-7, and nickel at pH = 6-9, and precipitate in the organophosphorus compound: copper at pH > 7, cobalt at pH ≥ 8, and nickel at pH ≥ 10. The possibility of separation of copper (II) and cobalt (II) is insignificant, the stripping of copper (II) and nickel (II) happens at pH = 4-6, and the stripping of cobalt (II) and any of nickel (II) – at pH = 5-6. The obtained results of ion extraction of the investigated metals can be used not only for processing of technological solutions, but also for purification of effluents from industrial enterprises and mine waters, heap and underground leaching solutions, etc. from the ions of studied metal ions

MAPPING OF ECOLOGICALLY VULNERABLE ZONES AND REGIONS OF WATER AREAS AND SHORELINES WITH PRIORITY PROTECTION AGAINST SPILLS OF OIL AND OIL PRODUCTS IN RUSSIA

Map development for ecologically vulnerable zones and regions of water areas and shorelines with priority protection against spills of oil and oil products is important because of (1) the population’s concern about the growing technological load on nature, and (2) the need to comply with the existing state legislation. At present there is no general methodology for development of vulnerability maps in Russian Federation. The integral maps to be used in prevention and control of oil spills should represent data about ecological vulnerability to oil of both coastal and water ecosystems and information about legally protected objects, zones and regions. A set of maps showing absolute and relative integral vulnerability of particular water areas allows analyzing spatial-temporal dynamics of this indicator. The most vulnerable areas (regions) of the water area could be selected, as well as the most dangerous seasons. Recommendations are elaborated in order to organize the most effective protection of the environment against any possible emergency spills of oil and oil products

Methods of histogram transformations and control processes of printing image reproduction

В статье предлагаются новые методы, позволяющие провести объективную оценку растровых структур по статистическим параметрам гистограммы, и метод коррекции изображения с использованием преобразования гистограммы по нормальному закону распределения, позволяющий автоматизировать процесс коррекции.There are new methods helping to do objective valuation of screen structures on statistical parameters of the histogram and method of image correction using histogram conversion with Gaussian distribution, allowing to automate correction process in our article