Local Geometric Distortions Research Articles

Still-image watermarking robust to local geometric distortions

Geometrical distortions are the Achilles heel for many watermarking schemes. Most countermeasures proposed in the literature only address the problem of global affine transforms (e.g., rotation, scaling, and translation). In this paper, we propose an original blind watermarking algorithm robust to local geometrical distortions such as the deformations induced by Stirmark. Our method consists in adding a predefined additional information to the useful message bits at the insertion step. These additional bits are labeled as resynchronization bits or reference bits and they are modulated in the same way as the information bits. During the extraction step, the reference bits are used as anchor points to estimate and compensate for small local and global geometrical distortions. The deformations are approximated using a modified basic optical flow algorithm.

Automatic Registration of Airborne Images with Complex Local Distortion

Accurate registration of airborne images is challenging because complex local geometric distortions are often involved in image acquisition. In this paper, we propose a solution to this registration problem in two parts. First, we present an area-based method to extract sufficient numbers of well-located control points, and second, we use the extracted control points with local transformation models to register multi-temporal airborne images. The proposed image registration methods were applied to two airborne images with complex local distortion. Performance was evaluated and compared using different transformation models (global models and local models), different numbers of control points, and different similarity measures (correlation coefficient and mutual information). The results showed that local models outperformed global models, more control points could significantly improve local transformation models but not on the global transformation models, and two similarity measures performed similarly. These results revealed two important findings: first, the area-based methods generated larger amounts of evenly distributed control points; and second, local transformation models achieved better registration accuracy when larger amount of evenly distributed control points are used. We concluded that the combination of area-based control point extraction with local transformation models is effective for the registration of airborne images with complex local distortion.

Connectivity-Based Image Watermarking

A novel robust watermarking scheme based on image connectivity is proposed. Having obtained the connected objects according to the selected connectivity pattern, the gravity centers are calculated in several larger objects as the reference points for watermark embedding. Based on these reference points and the center of the whole image, several sectors are formed, and the same version watermarks are embedded into these sectors. Thanks to the very stable gravity center of the connected objects, watermark detection is synchronized successfully. Simulation results show that our scheme can survive under both local and global geometrical distortions.

Investigation of the mica x-ray absorption near-edge structure spectral features at the AlK-edge

Near-edge features of Al x-ray absorption near-edge structure (XANES) spectra inaluminosilicate compounds with mixed coordination number are usually assigned to afourfold coordinated site contribution followed by a sixfold coordinated site contributionthat is displaced towards higher energy because of the increasing ligand nucleuspotentials, neglecting possible contributions due to bond distance variations and localgeometrical distortion. Here we present and discuss the Al K-edge XANES spectra ofsynthetic micas with either fourfold coordinated Al (phlogopite), or with sixfoldcoordinated Al (polylithionite), as well as with mixed coordination (preiswerkite).Multiple scattering simulations of XANES spectra demonstrate that octahedralcontributions may overlap the tetrahedral ones so that the lower energy structuresin mixed coordination compounds may be associated with the octahedral sites.This unexpected behaviour can be described as due to the effect of a significantreduction of the ligand field strength (i.e. large local distortion and Al–O bonddistances).

Prevention of focal intimal hyperplasia in rat vein grafts by using a tissue engineering approach

The present study focused on the role of blood flow in the formation of focal intimal hyperplasia in vein grafts, as well as the development of an engineering approach that can be used to eliminate disturbed blood flow and prevent blood flow-related focal intimal hyperplasia. A rat vein graft model was constructed by interposing a jugular vein into the abdominal aorta with end-to-end anastomoses. Locally disturbed flow was identified by analyzing particle streak-lines in methyl salicylate-cleared and perfused vein grafts in vitro with a physiological Reynolds number. At day 10, 20, and 30 after surgery, focal intimal hyperplasia of the vein grafts was examined using a histological approach and the density of α-actin positive cells was determined using immunohistological and fluorescent approaches. Results showed that apparent eddy blood flow formed at the proximal, but not at the distal, end of the vein grafts due to graft-host diameter mismatch and local geometric distortions, and was associated with apparent focal intimal hyperplasia. The thickness of the α-actin positive layers of the proximal vein grafts was significantly higher than that of the distal grafts (192±27 vs. 94±18 μm, 278±55 vs. 124±20 μm, and 288±24 vs. 131 ±23 μm for day 10, 20, and 30, respectively). The density of the α-actin positive cells, however, was similar between the proximal and the distal regions (3569±361 vs. 3285±343 cells/mm 2, 5540±650 vs. 5376±887 cells/mm 2, and 5465±791 vs. 5278±524 cells/mm 2 for day 10, 20, and 30, respectively). When eddy blood flow was eliminated by matching the graft-host diameters using a tissue engineering approach, the average thickness of the α-actin positive layers of the proximal (71±15, 86±16, and 85±14 μm for day 10, 20, and 30, respectively) and the distal vein grafts (68±13, 80±14, and 79±13 μm for day 10, 20, and 30, respectively) was reduced significantly. The density of the α-actin positive cells was also reduced significantly in the proximal (2946±359, 3261±295, 3472±599 cells/mm 2 for day 10, 20, and 30, respectively) and in the distal regions (3151±511, 3466±687, 3593±688 cells/mm 2 for day 10, 20, and 30, respectively). The thickness of the α-actin positive layers and the density of the α-actin positive cells were not significantly different between the proximal and distal regions of the engineered vein grafts at each observation time. These results suggest that eddy flow may develop in vein grafts and may facilitate the formation of focal intimal hyperplasia, and the vascular tissue engineering approach developed in this study may be used to prevent blood flow-related focal intimal hyperplasia in vein grafts.

Gabor wavelet representation for 3-D object recognition

This paper presents a model-based object recognition approach that uses a Gabor wavelet representation. The key idea is to use magnitude, phase, and frequency measures of the Gabor wavelet representation in an innovative flexible matching approach that can provide robust recognition. The Gabor grid, a topology-preserving map, efficiently encodes both signal energy and structural information of an object in a sparse multiresolution representation. The Gabor grid subsamples the Gabor wavelet decomposition of an object model and is deformed to allow the indexed object model match with similar representation obtained using image data. Flexible matching between the model and the image minimizes a cost function based on local similarity and geometric distortion of the Gabor grid. Grid erosion and repairing is performed whenever a collapsed grid, due to object occlusion, is detected. The results on infrared imagery are presented, where objects undergo rotation, translation, scale, occlusion, and aspect variations under changing environmental conditions.

Electronic structure of Ti3+ in BeAl2O4

Two different kinds of assignment of energy levels for the Ti3+ ion and its local geometrical distortion in BeAl2O4 were suggested by experimental researchers. To check which is reasonable, first-principles calculations are performed on the electronic structure of Ti3+ with four cluster models. The study supports the energy-level diagram suggested by Sugimoto et al. A distorted configuration of the cluster (TiO6)9- is proposed, with which experimental data can be satisfactorily explained and for which various electronic properties such as energy levels, density of states, orbital populations, charge distribution and spin polarization splitting are presented.

An adaptive method for image registration

The paper deals with the registration of images with non-linear local geometric distortions. It describes a new approach to the determination of a mapping function from given coordinates of control points. The processed image is recursively divided into subregions of various size and shape according to the distortion character. Each subregion is then transformed by a simple local transformation. The described method enables the registration with optional accuracy. A practical use of this method is presented and a comparison of its accuracy and computing complexity with previously published methods is given.

A study of model energetics and conformational properties of polynucleotide triplexes

The formation of triple-stranded nucleic acid helices is studied by molecular mechanics and molecular dynamics calculations. Using standard TAT and CGG homopolymers, single, triple, and quintuple molecular replacements are made. Some of these replacements are expected to form Hoogsteen bonds and some are not. While the electrostatic and total energetic differences for base triplet mismatches were dependent on the electrostatic model chosen, clear trends in the local geometric distortions were apparent. Relationships between these model-built strand geometries and chemical probe experiments are discussed.

Electronic properties of a realistic model of amorphous silicon.

We present the results of a first-principles calculation of the electronic density of states for a large, realistic model of amorphous silicon (a-Si). The structural basis of the calculation is a 216-atom, fully-fourfold-coordinated model of a-Si with periodic boundary conditions, whose pair-correlation function, average geometric distortions, and vibrational properties are in good agreement with experiment. The calculation is carried out by using the recursion method in conjunction with the tight-binding linear muffin-tin orbitals scheme in its simplest form. To assess the accuracy of our results, we apply the method to a crystalline silicon cluster and obtain a density of states similar to that obtained with the conventional Brillouin-zone summation method. The valence-band density of states calculated for the a-Si model shows good overall agreement with that measured for a-Si by x-ray photoelectron spectroscopy. The Si 3p valence-band peak is found to shift by 0.5 eV to lower binding energy compared with its position in the crystal, and the Si 3s and ``s-p'' hybrid bands of the crystal merge into one broad band in the amorphous model. We examine the local density of states of several atoms in the center of the cluster and the charge content of the corresponding atomic spheres to determine the effects of geometric distortion on the density of states and the degree of local distortion-induced static charge transfer. The rms static charge deviation is 0.14e, which is in good agreement with the experimental value of 0.11e. We find that neither particular features in the local densities of states nor the charge deviations from the mean of atoms in the center of the a-Si unit cell are correlated with the surrounding local geometric or topological distortions. Sharp peaks in the spectral functions of the a-Si model indicate remnants of the E-k dispersion relations for both s- and p-like states near k\ensuremath{\approxeq}0. The peaks broaden for larger values of k, in agreement with the dispersion behavior in disordered semiconductors suggested by Ziman.

Registration of images with geometric distortions

A technique for registration of images with geometric distortions is described. This technique uses two surface splines to represent the X-component and the Y-component of a mapping function. A mapping function is described in such a way that it would map corresponding control points in the image exactly on top of each other and map other points in the image by interpolation using information and local geometric distortion between the images.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Effects of Coordination and Local Disorder on Impurity States in Hydrogenated Amorphous Silicon

AbstractThe self-consistent pseudopotential method has been used to calculate the electronic structure of a periodic model of hydrogenated amorphous silicon containing, independently, P and B impurities. We have investigated both impurities in threefold- and fourfold-coordinated sites. Both types of sites studied also include the realistic distortion inherent in disordered systems. In fourfold coordination, both P and B introduce gap states, the energy and spatial extent of which depend upon the local geometrical distortion. In threefold coordination, the lone pair state of P is found below the valence band edge, while the B non-bonding state is found above the conduction band edge. The effects of local geometrical distortion on both of these states is also discussed. Comparisons with other calculations and experimental results are made.

A model for the structure of metallic glasses based on chemical twinning

A model for transition-metal-metalloid glasses has been constructed and refined by energy minimization with the use of a Lennard-Jones 6-12 potential. The model is based on the concept that domains of positionally correlated atoms exist in these glasses on a scale of 1-2 nm. Within each domain, positional order is governed by rules appropriate to a single type of structural operation (simple chemical twinning in this case) acting in a prescribed direction. (The structure of compositionally equivalent crystalline phases may be represented by similar rules acting over essentially infinite domains.) Positions of atoms in the interface between domains are defined by two (or more) operations appropriate to each of the bounding domains so that the structure has a high degree of homogeneity. Computed properties are compared with experimental structural data for a number of typical amorphous transition-metal-metalloid alloys. Agreement between experimental and calculated partial pair-correlation functions and structure factors is good, supporting the notion of extensive local and medium-range positional order in these alloys. Moreover, the discrepancies that exist between model data and experimental results suggest that the model is less ordered than an actual glass. This model provides some insight into the nature of local geometrical distortions of structural units, coupling between positional and compositional fluctuations and the relative stability of glassy and microcrystalline alloys.

15N‐NMR study of activated enamines. Structural dependence of δ (15N) and nJ(N,H) in primary, secondary and tertiary enamino‐ketones, esters and amides

AbstractThe pulse sequence INEPT was used to obtain proton‐coupled 15N‐NMR spectra in natural isotope abundance for enamines substituted in 2‐position with electron‐with‐drawing groups.The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N‐alkyl substitution, double‐bond configuration, H‐bonding, N‐lone‐pair delocalization within the conjugated system, and steric effects.It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N‐atom and conformational changes in a remote part of a conjugated molecule, while one‐bond N,H‐coupling essentially reflects N‐hybridization and subtle local geometric distortions. Stereospecific three‐bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)‐isomers in all investigated compounds, whereas two‐bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)‐isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the CN bond.