Nikolay Kirov

IR Spectroscopic investigations of peculiar behaviour of 4,n-alkoxybenzoic acids in their mesomorphic state I. Non-aligned samples

Abstract The equilibrium concentration of cyclic dimers, open dimers and monomers in 4,n-heptyloxybenzoic acid (HOBA) has been determined by IR spectroscopic investigations. It was found that the evolution of correlation between these molecular forms upon temperature variation provokes a strong textural transition in the nematic phase at temperature T*. The decisive role of local orientational order in the process of formation and destruction of hydrogen bonds is discussed. In addition, the shift of T* caused by bulk deformation of the nematic phase of HOBA on the basis of temperature variation of dimer-monomer concentration is considered as well. A new peculiar temperature (T f ) was found in the nematic phase where maximal dispersion in the temperature dependence of the cyclic and open dimer concentration is established. Strong textural oscillation is observed at that temperature.

Word Image Matching Based on Hausdorff Distances

Hausdorff distance (HD) and its modifications provides one of the best approaches for matching of binary images. This paper proposes a formalism generalizing almost all of these HD based methods. Numerical experiments for searching words in binary text images are carried out with old Bulgarian typewritten text, printed Bulgarian Chrestomathy from 1884 and Slavonic manuscript from 1574.

Volterra series and numerical approximations of ODEs

A numerical approach for solving systems of nonautonomous ordinary differential equations (ODEs) is proposed under suitable assumptions. This approach is based on expansion of the solutions of ODEs by Volterra series and allows to estimate the distance between the obtained approximation and the true trajectory.

Fourier transform far-infrared spectroscopy of the hydrogen bond in 4-n-alkoxybenzoic acids

Abstract Far-infrared transmittance spectra (200-30 cm−1) of the hydrogen bond in cyclic dimers of 4-n-heptyl-, octyl- and nonyloxybenzoic acids are observed and investigated. The spectral bands at 42, 63, 68 and 82 cm−1 are assigned to the four deformation vibrations: twisting, bending (in and out of the dimer ring plane) and stretching by halfwidth spectral band temperature analysis. The hydrogen band evolution in the isotropic and nematic phases is investigated. A cyclic ↔ open dimer transformation at different vibration frequencies and polarizations is shown. The critical character of the temperature T ∗ , defined as the temperature dividing the nematic phase of the nematics with hydrogen-bonded molecules into high-temperature (classical) and low-temperature (smectic-like) subphases, is demonstrated.

Corrections to orientational order parameters obtained by fluorescence measurements

Abstract The importance of various factors for the correctness and reliability of the orientational order parameters obtained by fluorescence measurements is discussed and experimentally verified with 4-dimethylamino 4′-nitrostilbene dye dissolved in N-(4-ethoxybenzylidene) 4′-butylaniline. All results demonstrate that only a careful consideration of all factors exerting influence on 2 > and data will give correct values for the orientational order parameters.

Text search in document images based on Hausdorff distance measures

The Hausdorff type distances between the sets of points on the plane are the commonly used similarity measures for binary images. In this work we present several such measures in a unified manner and introduce a new, naturally arisen variant of Hausdorff distance. The matching performance of all similarity measures is compared by computer experiments, using real word images from a scanned book.

Big data techniques, systems, applications, and platforms: Case studies from academia

Big data is a broad term with numerous dimensions, most notably: big data characteristics, techniques, software systems, application domains, computing platforms, and big data milieu (industry, government, and academia). In this paper we briefly introduce fundamental big data characteristics and then present seven case studies of big data techniques, systems, applications, and platforms, as seen from academic perspective (industry and government perspectives are not subject of this publication). While we feel that it is difficult, if at all possible, to encapsulate all of the important big data dimensions in a strict and uniform, yet comprehensible language, we believe that a set of diverse case studies - like the one that is offered in this paper - a set that spreads over the principal big data dimensions can indeed be beneficial to the broad big data community by helping experts in one realm to better understand currents trends in the other realms.

Higher Order Approximations of Affinely Controlled Nonlinear Systems

An numerical approach for numerical approximation of trajectories of a smooth affine control system is proposed under suitable assumptions. This approach is based on expansion of solutions of systems of ordinary differential equations (ODE) by Volterra series and allows to estimate the distance between the obtained approximation and the true trajectory.

Phase transitions and orientationial order parameters of N-(4-alkoxybenzylidene) 4′-toluidines in their mesomorphic states

Abstract The temperatures and the enthalpies of the phase transitions between the mesomorphic states formed upon cooling and heating of N-(4-alkoxybenzylidene) 4′-toluidines are treasured. The temperature dependence of the orientatioral order parameters 2 > and 4 > is reported. The observed even-odd alternation with the length of the paraffinic alkyl tail is discussed.