Effects Of Geometric Distortion Research Articles

Locally adaptive template sizes for matching repeat images of Earth surface mass movements

This paper presents an algorithm for locally adaptive template sizes in normalized cross-correlation (NCC) based image matching for measuring horizontal surface displacements of mass movements. After adaptively identifying candidate templates based on the image signal-to-noise ratio (SNR), the algorithm iteratively looks for the size at which the maximum cross-correlation coefficient attains a local peak and the matching position gets fixed. The algorithm is tested on modeled (deformed) images and applied to real bi-temporal images of different Earth surface mass movements. It is evaluated in comparison with globally (image-wide) fixed template sizes ranging from 11 to 101pixels based on the improvement in the accuracy of displacement estimation and the SNR of image reconstruction. The results show that the algorithm could reduce the error of displacement estimation by up to over 90% (in the modeled case) and improve the SNR of the matching by up to over four times compared to the globally fixed template sizes highly reducing the effects of geometric distortion and noise. The algorithm pushes terrain displacement measurement from repeat images one step forward towards full automation.

SU‐E‐J‐81: MR‐Based Prostate Radiotherapy Treatment Planning: An Investigation of the Dosimetric Consequences of Distortion Correction

Purpose: To quantify the effect of geometric distortions on patient dosimetry for MR‐based radiotherapy treatment planning (MR‐RTP) and to evaluate the clinical importance of distortion correction. Methods and Materials: Ten prostate patients underwent MR imaging in the standard treatment position. Axial MR images (MRIs) were segmented for bone and tissue, bulk electron densities were assigned, and images were corrected for machine‐ and patient‐related image distortion. Intensity modulated plans (IMRT) were developed for each patient and dose distributions were calculated on both the original and corrected images. The effect of MR distortion correction on both target and organ at risk (OAR) dosimetry was studied. Results: Maximum and mean image distortion for all patients was 5.4 mm and 1.4 mm, respectively. Distortions near the target and OARs were considerably less. The minimum dose received by the planning target volume (PTV) was most affected by distortion correction and changed, on average, by −0.3% for IMRT plans. Changes in mean and maximum PTV dose were smaller and dose volume histograms (DVHs) were insignificantly altered. Conclusions: For the combination of the MR scanner and imaging sequence, distortion correction has no impact on prostate plan dosimetry when patients are properly positioned within the magnet. MR‐RTP will be further studied but appears to be clinically viable for prostate patients.

Spin transitions in semiconductor quantum rings

We adopt the path integral Monte Carlo method to accurately resolve the total spin of the ground state of electrons confined in a quantum ring with different geometries. Using this method, an evaluation of the ground state of three electrons in a ring shows a spin transition to the fully polarized state by increasing the radius and thereby enhancing the Coulomb interaction. The total spin of the ground state is determined by the mutual interplay of confinement and electron-electron interaction. An analysis of the four-electron ring demonstrates that in this case no spin transitions take place. Furthermore, the effect of geometric distortion of the ring on its ground state has been investigated. Elliptically deforming the ring breaks the symmetry of the system and leads to the removal of orbital degeneracy. For strong distortion the splitting between hybridized states is sufficient to overcome the exchange-energy saving associated with a higher spin state. We have found that this effect removes the polarization of three electrons. Even in a four-electron ring the ground state is forced by the distortion to be unpolarized and thus suppressing the Hund's rule ground state.

Adsorption of cobalt (II) octaethylporphyrin and 2H-octaethylporphyrin on Ag(111): new insight into the surface coordinative bond

The adsorption of cobalt (II) octaethylporphyrin (CoOEP) and 2H-octaethylporphyrin (2HOEP) on Ag(111) was investigated with scanning tunneling microscopy (STM) and photoelectron spectroscopy (XPS/UPS), in order to achieve a detailed mechanistic understanding of the surface chemical bond of coordinated metal ions. Previous studies of related systems, especially cobalt (II) tetraphenylporphyrin (CoTPP) on Ag(111), have revealed adsorption-induced changes of the oxidation state of the Co ion and the appearance of a new valence state. These effects were attributed to a covalent interaction of the Co ion with the silver substrate. However, recent studies show that the porphyrin ligand of adsorbed CoTPP undergoes a pronounced saddle-shape distortion, which could alter the electronic structure and thus provide an alternative explanation for the new valence state previously attributed to the formation of a surface coordinative bond. With the octaethylporphyrins investigated here, which were found to adsorb in a flat, undistorted conformation on Ag(111), the effects of geometric distortion can be separated from those of the electronic interaction with the substrate. The CoOEP monolayer gives rise to an adsorption-induced shift of the Co 2p signal (−1.9 eV relative to the multilayer), a new valence state at 0.6 eV below the Fermi energy, and a work-function shift of −0.84 eV (2HOEP: −0.44 eV) relative to the clean surface. Comparison with data for the distorted CoTPP confirms the existence of a covalent ion–surface interaction that is insensitive to the conformation of the ligand.

Geometry Dependence of the Ring-Opening E2 Reaction in Lactones

Gas phase bimolecular elimination reactions (E2) of lactones, with and without alkyl substitution on the omega carbon, have been studied. The comparison between the substituted and corresponding unsubstituted lactones reveals, without complications from ring strain, the effect of geometric distortion from the periplanar geometry preferred for E2 reactions. The four- and five-membered ring lactones show a significant effect from the distortion, while the six- and seven-membered rings show relatively little. The geometric distortion is clearly much more important than the ring strain. The kinetic energy dependence of the E2 reaction as well as the proton transfer reaction between fluoride and a partially deuterated delta-valerolactone has also been investigated.

Improving the concordance between various anteroposterior cephalometric measurements using Procrustes analysis

The aim of this study was to investigate a method which minimizes the effects of geometric distortion on various cephalometric measurements used to determine sagittal discrepancy, such as ANB angle, Wits appraisal, AB plane angle, projections on the palatal plane, Frankfort horizontal (FH) plane, the mandibulomaxillary bisector, and the SN line, in an attempt to optimize the correlation between them. This was accomplished by superimposing the Bolton 12-year male-female averaged template on a patient's tracing using Procrustes analysis and performing measurements while exchanging the patient's reference landmarks/planes (point N, the mandibulomaxillary bisector, FH plane, occlusal plane, palatal plane, and SN line) with those of the template. The normalized measurements were then compared with their classic counterparts using correlation coefficients. The above cephalometric analyses, classic and normalized, were applied to 71 patients [26 males: mean age 13.1 years, standard deviation (SD) 1.1 years and 45 females: mean age of 14.6 years, SD 8.2 years]. Spearman's rank correlation coefficient was calculated between the classic measurements and their normalized counterparts, resulting in a consistent increase in the correlation between the normalized measurements in comparison with the classic ones. This increase varied in absolute value from 0.052 to 0.405. All normalized measurements were highly correlated (P > 0.742, absolute value). Although correlation calculations do not represent a true measure of diagnostic performance, it is hoped that improving their correspondence heightens the possibility of the different tests agreeing on the patient's sagittal discrepancy, decreasing the possibility of differing, or even totally opposing diagnostic outcomes resulting from their application to (clear-cut) Class I, II, and III patients.

Simulation of hydrogen bonding in biological systems: Ab initio calculations for NH3NH3 and NH3NH4+

Ab initio calculations by Pople's 4–31G method are reported for (NH3)2 and for NH3(NH4−) in order to study the effects of geometric distortions upon NHN hydrogen bonds. The optimum nitrogen-nitrogen separations are found to be 3.37 and 2.79 Å for linear hydrogen bonds in the ammonia dimer and ammonia ammonium systems, respectively. The variation in energy with distance is well fit by Morse functions in both cases. Energy losses due to displacements of the electron donating NH3 and due to nonlinearity in the N–H–N bond are also discussed.

Super-Resolution of Remotely Sensed Images With Variable-Pixel Linear Reconstruction

This paper describes the development and applications of a super-resolution method, known as Super-Resolution Variable-Pixel Linear Reconstruction. The algorithm works combining different lower resolution images in order to obtain, as a result, a higher resolution image. We show that it can make significant spatial resolution improvements to satellite images of the Earth's surface allowing recognition of objects with size approaching the limiting spatial resolution of the lower resolution images. The algorithm is based on the Variable-Pixel Linear Reconstruction algorithm developed by Fruchter and Hook, a well-known method in astronomy but never used for Earth remote sensing purposes. The algorithm preserves photometry, can weight input images according to the statistical significance of each pixel, and removes the effect of geometric distortion on both image shape and photometry. In this paper, we describe its development for remote sensing purposes, show the usefulness of the algorithm working with images as different to the astronomical images as the remote sensing ones, and show applications to: 1) a set of simulated multispectral images obtained from a real Quickbird image; and 2) a set of multispectral real Landsat Enhanced Thematic Mapper Plus (ETM+) images. These examples show that the algorithm provides a substantial improvement in limiting spatial resolution for both simulated and real data sets without significantly altering the multispectral content of the input low-resolution images, without amplifying the noise, and with very few artifacts

Effects of element distortions on the performance of enriched quadrilateral elements

It is well known that the accuracy of finite element solutions deteriorate in the presence of severe mesh distortions. But distortion is often unavoidable in mesh procedure involving complex geometry. Lee and Bathe (1993) studied the influence of mesh distortion on the serendipity and Lagrange quadrilateral elements. Lautersztajn and Samuelsson (2000) discussed the effects of geometric distortions on four-node isoparametric quadrilateral elements and concluded that the element performance can be rendered ?insensitive? to a particular type of mesh distortion by increasing the order of the interpolation functions for the displacement field. In order to overcome the influence of element distortions, unsymmetric 8-node (Rajendran and Liew 2003) and unsymmetric 20-node element (Ooi et al. 2004) are developed to reproducing any linear and quadratic displacement field under any admissible mesh distortions. However, they will produce an asymmetrical stiffness matrix, so these formulations require an asymmetrical solver to solve the resulting stiffness equations. The goal of this paper is to discuss the effects of element distortions on the accuracy and efficiency of enriched quadrilateral elements with bubble functions. A bubble function is defined as a function that vanishes along the element boundaries. Bubble functions have been introduced to construct plate element models (Auricchio and Taylor 1995, Cook et al. 2002, Hong et al. 2001). They are employed to solve advection-diffusion problems by Brezzi, Franca and Farhat (Brezzi et al. 1992, Brezzi and Russo 1994, Franca and Farhat 1995). Furthermore, the limitation of bubble functions is discussed by Franca and Farhat (1994) and error analysis of residual-free bubbles is discussed by Brezzi et al. (1999) and Sangalli (2000).

P-91: Technology of Spontaneously Forming Multidomains for Wideviewing Angle LCDs

We demonstrated a spontaneously formed multidomain structure for wideviewing liquid crystal displays(LCDs). The multidomain structure was obtained by inserting an alignment film having periodically embedded patterns into the LC cell. Since the suggested alignment film has no morphological modulation on the LC interface, the reorientation of the LC director is precisely controlled by the electric field distortion effect without any geometric distortion effect on the surface. The symmetrical distortion of an applied electric field enhances wideviwing characteristics.

A Valence Bond Description of Coordinate Covalent Bonding

The coordinate covalent (dative) bonded molecules H3N−BH3, H3N−BF3, F3N−BH3, H3N−BMe3, and Me3N−BH3 have been studied using valence bond theory (VB). The classic three-structure VB picture changes slightly to account for the increased importance of the VB configuration with both electrons on the donor fragment. When the effects of geometric distortion upon molecule formation are removed, the expected trends in bond energies emerge. Addition of electron-withdrawing (F) substitutents increases bond energy in H3N−BF3 and decreases bond energy in F3N−BH3. Likewise, addition of electron-donating methyl groups (Me) decreases bond energy in H3N−BMe3 and increases bond energy in Me3N−BH3. In addition, the effects of adding fluorines stepwise in the series H3N−BH3, H3N−BH2F, H3N−BHF2, H3N−BF3 has been determined. Bond energies are due to the opposing factors of electron withdrawal due to the high fluorine electronegativity and donation into the N−B bonding region by F p lone pairs. VB weights obtained by the method of Chirgwin and Coulson were unstable for coordinate covalently bonded molecules whereas no such problems were found for inverse overlap weights. VB weights in conjunction with bond energy partitioning show that the coordinate covalent bonds studied herein are predominantly charge shift bonds which owe their stability to VB structure mixing rather than any one structure alone.

Effects of geometric distortion in 0.2 T MRI on radiotherapy treatment planning of prostate cancer

Background and purpose To evaluate the impact of two different methods of geometric distortion correction of MR images from a Siemens Magnetom Open Viva 0.2 T resistive MR unit on the process of external beam radiotherapy treatment planning for prostate cancer. Patients and methods A method for correction of system related and object induced distortions and one for correction of purely system related distortions have been evaluated. The latter used information extracted from MR images of a 3D phantom specifically designed for geometric distortion evaluation. An active shim procedure was performed prior to all phantom and patient scans. For each of five patients five standard treatment plans were compared using uncorrected and corrected MR images alone (density=water) and CT images alone. Finally internal anatomical landmarks were used for image registration between MR images (corrected and uncorrected) and CT images to evaluate the impact of distortion correction on the image registration process. Results Maximum distortions of 28 mm (mean 2.2 mm) were found within the FOV in frequency encode direction. Maximum distortions could be reduced by a factor of two (mean factor four) by our phantom measurement based technique. Distortion patterns were found to be stable and reproducible over several weeks with this MR unit. For 4/5 patients, relative doses at the normalization point as calculated on the distortion corrected MR images only (all tissues taken water equivalent) were all within 1% of the corresponding value from the standard CT-based plan (actual Hounsfield units). The largest differences in isocentric dose found in one case were 3.1% MR uncorrected vs. CT and 2.6% MR corrected vs. CT. Typical sites of internal anatomical landmarks chosen for image registration show distortions up to 3 mm. Conclusions Object induced distortions are negligible at such low field strengths compared to system related distortions. Treatment plans for prostate cancer do not seem to differ significantly from ‘standard’ plans calculated on CT images when calculated on distortion corrected MR images, even if all tissues are assigned the electron density of water. Distortion correction of MR images can theoretically improve the starting point for image registration of MR and CT images.

253 poster Effects of geometric distortion in pelvic MRI on radiotherapy treatment planning of prostate cancer patients

253 poster Effects of geometric distortion in pelvic MRI on radiotherapy treatment planning of prostate cancer patients

Effects of geometric distortions on face-recognition performance.

The importance of 'configural' processing for face recognition is now well established, but it remains unclear precisely what it entails. Through four experiments we attempted to clarify the nature of configural processing by investigating the effects of various affine transformations on the recognition of familiar faces. Experiment 1 showed that recognition was markedly impaired by inversion of faces, somewhat impaired by shearing or horizontally stretching them, but unaffected by vertical stretching of faces to twice their normal height. In experiment 2 we investigated vertical and horizontal stretching in more detail, and found no effects of either transformation. Two further experiments were performed to determine whether participants were recognising stretched faces by using configural information. Experiment 3 showed that nonglobal vertical stretching of faces (stretching either the top or the bottom half while leaving the remainder undistorted) impaired recognition, implying that configural information from the stretched part of the face was influencing the process of recognition--ie that configural processing involves global facial properties. In experiment 4 we examined the effects of Gaussian blurring on recognition of undistorted and vertically stretched faces. Faces remained recognisable even when they were both stretched and blurred, implying that participants were basing their judgments on configural information from these stimuli, rather than resorting to some strategy based on local featural details. The tolerance of spatial distortions in human face recognition suggests that the configural information used as a basis for face recognition is unlikely to involve information about the absolute position of facial features relative to each other, at least not in any simple way.

Drizzle: A Method for the Linear Reconstruction of Undersampled Images

ABSTRACTWe have developed a method for the linear reconstruction of an image from undersampled, dithered data. The algorithm, known as Variable‐Pixel Linear Reconstruction, or informally as “Drizzle,” preserves photometry and resolution, can weight input images according to the statistical significance of each pixel, and removes the effects of geometric distortion on both image shape and photometry. This paper presents the method and its implementation. The photometric and astrometric accuracy and image fidelity of the algorithm as well as the noise characteristics of output images are discussed. In addition, we describe the use of drizzling to combine dithered images in the presence of cosmic rays.

Solvatochromism in substituted 2,2′-bipyridinetetracarbonyl-metal complexes of chromium, molybdenum and tungsten

The influence of various solvents on the electronic absorption spectra in the visible region of complexes of the general type [M(CO) 4( n, n′-X 2-bipy)] (M = Cr, Mo, W; n = 3, 4, 5, 6; X = CH 3, CN, CO 2CH 3; bipy = 2,2′-bipyridine) has been measured. Molar absorption coefficients are reported. Attempts to correlate this information with the solvent polarity parameter proposed by Manuta and Lees indicate that the effects of geometric distortion in the substrate complex preclude a simple explanation of the observations in terms of a single parameter.

Bonding properties of penta-coordinate Cu II-N chromophores: structures and electronic spectra of copper(II) complexes of tris(2-aminoethyl)amine (tren). Molecular structures of [Cu(tren)(N-acetylhistamine)](ClO 4) 2 and [Cu(tren)(2-methylimidazole)](ClO 4) 2

Tris(2-aminoethyl)aminecopper(II) perchlorate complexes, [Cu(tren)L](ClO 4) 2 [tren is tris(2-aminoethyl)amine and L are neutral N-donor ligands including imidazoles, pyridines and amines], have been synthesized and characterized. The X-ray crystal structures of [Cu(tren)(achmH)](ClO 4) 2 ( 1) and [Cu(tren)(2MImH)](ClO 4) 2 ( 2) (achmH = N-acetylhistamine; 2MImH = 2-methylimidazole) have been determined. Their structures consist of discrete perchlorate anions and distorted trigonal-bipyramidal [Cu(tren)(N-donor)] 2+ cations with the three primary amine groups of the tren ligand forming the equatorial plane, where one of the equatorial angles is larger than the other two and the CuN opposite the largest equatorial NCuN angle is significantly longer than the other two. Electronic and EPR spectra are reported for these complexes. The LF spectra are analysed in trigonalbipyramidal symmetry with the Jahn-Teller effect being considered in the excited state and the effect of geometric distortions. The d-orbitals are assigned in a sequence of d z 2 >> d x 2-y 2 > d xy > d xz ≈ d yz . The bonding properties of the CuN 5 chromophores are elucidated and discussed with reference to the electronic structures of the complexes, suggesting no π-interaction in the axial CuN bonds.

Detection limits in quantitative off-axis electron holography

The phase of an electron wave is altered by electric and magnetic fields as it passes through a specimen. This phase change can be accurately quantified from off-axis electron holograms acquired using a slow-scan CCD camera, and small changes can be observed over small dimensions. Expressions for the precision of the phase estimate, which is limited by shot noise, have been developed. These include most of the real experimental parameters. It is found that the typical precision of practical phase measurements is better than π/100 for spatial resolutions of 1–3 nm, in good agreement with the theoretical optimal phase precision. In order to attain such small errors the effects of geometric distortion, which can introduce phase differences of up to π, must be carefully corrected.

Circular dichroism studies of distorted alpha-helices, twisted beta-sheets, and beta turns.

Theoretical models for calculating the circular dichroism (CD) of biopolymers have been constructed which allow the evaluation of the effects of geometric distortions within regular secondary structures. Outward tilting of the carbonyl group within alpha-helical structures yields calculated CD spectra with diminished intensity and a red-shifted maximum near 190 nm. The alpha II-helix provides an extreme example of this type of alpha-helix distortion. It is predicted that a mixture of alpha and alpha II structures in bacteriorhodopsin can account for its anomalous CD spectrum. The minimum length of alpha-helix required to produce an alpha-helix-like CD spectrum is calculated to be two to three turns (seven to eleven residues), while helices greater than 30 residues should provide adequate models of an infinite helix. Twisting of beta-sheets is predicted to lead to an increase in CD intensity and significant shifts in band position. Calculated CD spectra for beta-turn models are accurate for types II and II', but appear to be inadequate for type I turns.

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.