B. Pura

Reentrant Phases of Four-Ring Aromatic Esters

The results are described of microscopic, calorimetric and X-ray diffraction investigations of compounds of the general formula 1

X-Ray Diffraction Study of the Smectic I, F, J and G Phases of—4—2-Methy1Butyl Phenyl 4-n-Octybiphenyl-4-Carboxylate

Abstract The smectic I, F, J and G phases of the chiral ferroelectric compound (+)-(4-(2′-methylbutyl)phenyl 4′-n-octylbiphenyl-4-carboxylate) (+ 2M4P8BC) were studied by means of optical microscopy and X-ray diffraction. The free-standing film method was used. The films were additionally ordered with a d. c. electric field and true monodomain samples were prepared and examined.

X-Ray Investigations of +2M4P8BC Ferroelectric Liquid Crystals

Abstract The X-ray diffraction patterns from aligned smectics G*, J*, I* and C* of ferroelectric liquid crystal +2M4P8BC were obtaised by using electric field. New symmetry of molecular packing in plane normal to the molecular long axes for smectic I* is presented.

X-ray and optical investigations of ferroelectric +2M4P8BC liquid crystal

Abstract The ferroelectric compound 4-(2′-methylbutyl)phenyl 4′-n-octylbiphenyl-4-carboxylate (2M4P8BC) was studied by means of X-ray high pressure technique and polarized light microscopy.

Electro-optic guest-host system containing azobenzene chromophores in PMMA matrix

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Polymer‐based Photonic Modulator

In order to build a low‐cost light‐controlled waveguide modulating device, a new NLO polymer from the polyarylates group has been developed. The technology of the strip single‐mode waveguide patterns using this polymer has been elaborated. The Mach‐Zehnder interferometer geometry was used to evaluate the usefulness of the new material. Modulation effects were noticed even without polymer poling.

X-Ray Critical Scattering in Hexatic Smectic B - Smectic C Binary Mixture

Abstract We present the results of high-resolution X-ray scattering measurements for a binary mixture of smectic C; 4-hexyloxyphenyl-4-octylbenzoate and hexatic smectic B; 1-[5-(4-hexylphenyl)pyramidyl-2]-2-(4-hexyloxyphenyl) ethane. The Bragg scattering intensity was measured as a function of temperature for several concentrations x of smectic B. The molecular arrangement in the existing phases were determined. The smectic A phase (Ā) was observed which is strongly ordered by magnetic field and give very high diffraction peak. The smectic Ā - nematic phase transition was studied for concentrations x ≤ 0.3 including the vicinity of the NĀC point. The temperature dependence of the correlation lengths: Ξ↓2; - parallel to the long axes of the molecules and Ξ⊥ was discussed and critical indices: v ↓2;, v ⊥, and r were calculated.

The phase transitions and the X-ray critical scattering in the mixture of the liquid crystals SB+SC.

Abstract We have carried out a high-resolution X-ray critical scattering in a binary mixture of smectic B: 4-4-hexyl(bicyclo[2,2,2]octylphenyl) 4-octyl-oxybenzoate and smectic C: 1-[5-(4-hexylphenyl) pyrimidyl-2]-2-(4-hexylophenyl) ethane. Near the multicritical points NAC [1,2] and INA [3] the magnitudes of the critical exponents: v ↓2;,v ⊥ and r for the N - SA transition are extracted from our data. The critical exponent β was also calculated in the vicinity of the BAC and NAC points.

X-Ray Critical Scattering in the 4DBT/12DBT Binary Mixture Near the INA Point

Abstract The liquid crystal mixture of two SA smectics: 4DBT and 12DBT has been investigated by X-ray method. This compound exhibits an induced nematic phase for a molar fraction of 12DBT of 0.1 ≤ x ≤ 0.6. The smectic mass density fluctuations have been studied in the nematic phase near the INA point at x = 0.12. Values of the critical exponents: v ↓2;, v ⊥ and the anisotropy parameter Ξ↓2;/Ξ⊥ do not practically change with approaching the INA point along the smectic A - nematic transition line.