Eccentricity Of Cross Section Research Articles

Deciphering locomotion in reptiles: application of elliptic Fourier transforms to femoral microanatomy

Abstract Reptiles represent one of the most diverse groups of tetrapod vertebrates. Extant representatives of reptiles include lepidosaurs (lizards), testudines (turtles) and archosaurs (crocodiles and birds). In particular, they show an important locomotor diversity with bipedal, quadrupedal and facultatively bipedal taxa. This diversity is accompanied by substantial microanatomical disparity in the limb bones. Although many studies have highlighted the link between locomotion and bone microstructure, the latter has never been quantitatively studied from an angular perspective. Indeed, some taxa show microanatomical heterogeneity in cross-section. Here we show, using elliptic Fourier transforms and statistical analyses integrating phylogeny, how angular microanatomical parameters measured on reptilian femoral cross-sections, such as angular bone compactness, can be related to locomotion in this clade. Although phylogeny appears to have a significant impact on our results, we show that a functional signal exists. In particular, we show that bipeds and quadrupeds present a craniolateral-caudomedial and dorsoventral deficit in bone compactness, respectively. This reflects cross-sectional eccentricity in these directions that we relate to the forces acting upon the femur in different postural contexts. This work contributes to deciphering the complex interplay between phylogeny, femoral cross-sectional microanatomy and locomotion in reptiles.

Effect of Coupled Torsional and Transverse Vibrations of the Marine Propulsion Shaft System

In this study, the coupled torsional–transverse vibration of a propeller shaft system owing to the misalignment caused by the shaft rotation was investigated. The proposed numerical model is based on the modified version of the Jeffcott rotor model. The equation of motion describing the harmonic vibrations of the system was obtained using the Euler–Lagrange equations for the associated energy functional. Experiments considering different rotation speeds and axial loads acting on the propulsion shaft system were performed to verify the numerical model. The effects of system parameters such as shaft length and diameter, stiffness and damping coefficients, and cross-section eccentricity were also studied. The cross-section eccentricity increased the displacement response, yet coupled vibrations were not initially observed. With the increase in the eccentricity, the interaction between two vibration modes became apparent, and the agreement between numerical predictions and experimental measurements improved. Given the results, the modified version of the Jeffcott rotor model can represent the coupled torsional–transverse vibration of propulsion shaft systems.

Validation of Second-Generation Motion-Correction Software for Computed Tomography Coronary Angiography With Novel Quantitative Approach.

Computed tomography of the coronary arteries (CTCA) is an important diagnostic tool. However, motion degradation is sometimes a challenge to interpretation and quantification, particularly with elevated heart rates. Here, a novel quantitative method is presented as part of an evaluation of one particular motion correction algorithm. Computed tomography of the coronary arteries scans from 49 patients, with heart rates of >70 bpm, were identified with motion artifacts in multiple coronary segments. At these foci (196), an objective measure of motion degradation, defined here by cross-section eccentricity, was determined before and after image processing with second-generation GE SnapShot Freeze software (SSF-2.0). In addition, a subjective scoring was applied by an expert cardiothoracic radiologist both before and after processing. An overall decrease in vessel eccentricity strongly correlated (P < 0.001) with processing of the images by motion-correction software. A concurrent overall increase in subjective vessel clarity correlated (P < 0.001) with application of the software as well. A novel quantitative method (and subjective analysis) for evaluation of CTCA motion has been described and applied to validation of SSF-2.0 motion-correction software. Both the technique and software demonstrate promise for robust clinical utility in CTCA evaluation.

Influence of thoracic endovascular aortic repair on true lumen helical morphology for Stanford type B dissections

ObjectiveThoracic endovascular aortic repair (TEVAR) can change the morphology of the flow lumen in aortic dissections, which may affect aortic hemodynamics and function. This study characterizes how the helical morphology of the true lumen in type B aortic dissections is altered by TEVAR. MethodsPatients with type B aortic dissection who underwent computed tomography angiography before and after TEVAR were retrospectively reviewed. Images were used to construct three-dimensional stereolithographic surface models of the true lumen and whole aorta using custom software. Stereolithographic models were segmented and co-registered to determine helical morphology of the true lumen with respect to the whole aorta. The true lumen region covered by the endograft was defined based on fiducial markers before and after TEVAR. The helical angle, average helical twist, peak helical twist, and cross-sectional eccentricity, area, and circumference were quantified in this region for pre- and post-TEVAR geometries. ResultsSixteen patients (61.3 ± 8.0 years; 12.5% female) were treated successfully for type B dissection (5 acute and 11 chronic) with TEVAR and scans before and after TEVAR were retrospectively obtained (follow-up interval 52 ± 91 days). From before to after TEVAR, the true lumen helical angle (–70.0 ± 71.1 to –64.9 ± 75.4°; P = .782), average helical twist (–4.1 ± 4.0 to –3.7 ± 3.8°/cm; P = .674), and peak helical twist (–13.2 ± 15.2 to –15.4 ± 14.2°/cm; P = .629) did not change. However, the true lumen helical radius (1.4 ± 0.5 to 1.0 ± 0.6 cm; P < .05) and eccentricity (0.9 ± 0.1 to 0.7 ± 0.1; P < .05) decreased, and the cross-sectional area (3.0 ± 1.1 to 5.0 ± 2.0 cm2; P < .05) and circumference (7.1 ± 1.0 to 8.0 ± 1.4 cm; P < .05) increased significantly from before to after TEVAR. The distinct bimodal distribution of chiral and achiral native dissections disappeared after TEVAR, and subgroup analyses showed that the true lumen circumference of acute dissections increased with TEVAR, although it did not for chronic dissections. ConclusionsThe unchanged helical angle and average and peak helical twists as a result of TEVAR suggest that the angular positions of the true lumen are constrained and that the endografts were helically conformable in the angular direction. The decrease of helical radius indicated a straightening of the corkscrew shape of the true lumen, and in combination with more circular and expanded lumen cross-sections, TEVAR produced luminal morphology that theoretically allows for lower flow resistance through the endografted portion. The impact of TEVAR on dissection flow lumen morphology and the interaction between endografts and aortic tissue can provide insight for improving device design, implantation technique, and long-term clinical outcomes.

Multiaxial pulsatile dynamics of the thoracic aorta and impact of thoracic endovascular repair

PurposeThe thoracic aorta is a highly mobile organ whose dynamics are altered by thoracic endovascular aorta repair (TEVAR). The aim of this study was to quantify cardiac pulsatility-induced multi-axial deformation of the thoracic aorta before and after descending aortic TEVAR. MethodsEleven TEVAR patients (8 males and 3 females, age 57–89) underwent retrospective cardiac-gated CT angiography before and after TEVAR. 3D geometric models of the thoracic aorta were constructed, and lumen centerlines, inner and outer surface curves, and cross-sections were extracted to measure aortic arclength, centerline, inner surface, and outer surface longitudinal curvatures, as well as cross-sectional effective diameter and eccentricity for the ascending and stented aortic portions. ResultsFrom pre- to post-TEVAR, arclength deformation was increased at the ascending aorta from 5.9 ± 3.1 % to 8.8 ± 4.4 % (P < 0.05), and decreased at the stented aorta from 7.5 ± 5.1 % to 2.7 ± 2.5 % (P < 0.05). Longitudinal curvature and diametric deformations were reduced at the stented aorta. Centerline curvature, inner surface curvature, and cross-sectional eccentricity deformations were increased at the distal ascending aorta. ConclusionsDeformations were reduced in the stented thoracic aorta after TEVAR, but increased in the ascending aorta near the aortic arch, possibly as a compensatory mechanism to maintain overall thoracic compliance in the presence of reduced deformation in the stiffened stented aorta.

Influence of Thoracic Endovascular Aortic Repair on True Lumen Helical Morphology for Stanford Type B Dissections

Thoracic endovascular aortic repair (TEVAR) can change the morphology of the flow lumen in aortic dissections, which could affect aortic hemodynamics and function. The present study characterized how the helical morphology of the true lumen in type B aortic dissections is altered by TEVAR. Patients with type B dissection who had undergone computed tomography angiography before and after TEVAR were retrospectively recruited. The images were used to construct three-dimensional stereolithographic surface models of the true lumen and whole aorta using custom software (Fig 1). The stereolithographic models were segmented and co-registered to determine the helicity of the true lumen with respect to the whole aorta. The helical angle, helical radius, helicity (change of the helical angle over 3 cm using a sliding window), and cross-sectional eccentricity and area were quantified for the true lumen region covered by the endograft before and after TEVAR (Fig 1). Two-tailed paired t tests were used to compare the pre- and post-TEVAR metrics. Twelve patients (age, 61.75 ± 7.74 years; 8.3% women) had been treated successfully for complicated type B dissection with TEVAR (C-TAG; WL Gore & Associates, Newark, Del). From before to after TEVAR, the true lumen helical angle (−63° ± 70− to −58° ± 72°; P = .732) and peak helicity (−16° ± 15°/cm to −19° ± 12°/cm; P = .237) did not change significantly (Fig 2 and the Table). Both the true lumen average helical radius (1.37 ± 0.49 cm to 0.96 ± 0.55 cm; P = .001) and eccentricity (0.84 ± 0.15 to 0.66 ± 0.15; P = .002) had significantly decreased from before to after TEVAR. In contrast, the average cross-sectional area had increased significantly (from 3.22 ± 1.00 cm2 to 4.59 ± 1.58 cm2; P = .014). The unchanged helical angle and peak helicity as a result of TEVAR suggest that the proximal and distal portions of the region of interest were constrained to angular positions and the endografts used to treat this cohort were helically conformable in the angular direction. The decrease of the average helical radius indicated a straightening of the “corkscrew” shape of the true lumen, which might affect hemodynamics and aortic tissue stress. The effect of TEVAR on dissection flow lumen morphology and the interaction between endografts and aortic tissue will provide useful information for improving device design, implantation techniques, and long-term clinical outcomes.Fig 2Graph displaying how the helical angle, helical radius, true lumen eccentricity, and true lumen area vary longitudinally and how they are altered by thoracic endovascular aortic repair (TEVAR) for an example patient.View Large Image Figure ViewerDownload Hi-res image Download (PPT)TableQuantified metrics in region of interest before and after TEVARVariableBefore TEVARAfter TEVARP valueHelical angle, °−63 ± 70−58 ± 72.732Peak helicity, °/cm−16 ± 15−19 ± 12.237Average helical radius, cm1.37 ± 0.490.96 ± 0.55.001Average true lumen eccentricity0.84 ± 0.150.66 ± 0.15.002Average true lumen area, cm23.22 ± 1.004.59 ± 1.58.014TEVAR, Thoracic endovascular aortic repair.Boldface P values represent statistical significance. Open table in a new tab

Off-Centered Geometry and Influence on NiTi Endodontic File Performance Evaluated by Finite Element Analysis

The influence of cross-sectional eccentricity on the flexibility, torsional stiffness, and stress distribution in NiTi endodontic files was studied by finite element modeling. Three-dimensional (3D) models were built in order to reproduce commercial ProTaper Next X1 and X2 off-centered geometry instruments. Additionally, other 3D models with geometries similar to X1 and X2, but with concentric cross-sections, were created to isolate the eccentricity variable. The material properties and boundary conditions used in this study were the same for all instruments. The mechanical responses of each concentric/eccentric pair were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, off-centered files exhibit lower flexibility in comparison with their concentric counterparts. However, the eccentricity promoted a change in the stress distribution pattern so that the off-centered instruments showed lower maximum stress values under bending. Under torsional loads, no significant differences were observed. It is concluded that the mechanical and clinical advantages of an offset cross-section are not related to the increase of flexibility but rather to the optimization of the final diameter of the formatted root canal using instruments with lower mass. Also, there is a reduction in stress levels, increasing fatigue life, and improving the performance of the endodontic files.

Coronary Plaque Geometry and Thoracic Fat Distribution in Patients with Acute Chest Pain – a CT Angiography Study

Abstract The aim of our study was to investigate the correlation between volumes of thoracic fat distributed in different compartments and the geometry of vulnerable coronary plaques assessed by coronary computed tomography angiography (CCTA), in patients with acute chest pain. Methods: This was a non-randomized, observational, single-center study, including 50 patients who presented in the emergency department with acute chest pain who underwent 128-slice single-source CCTA. Plaque geometry was evaluated in transversal and longitudinal planes, and the assessment of adipose tissue was performed using the Syngo.via Frontier (Siemens AG, Healthcare Sector, Forchheim, Germany) research platform. Results: Eccentric plaques presented a significantly higher incidence of spotty calcification (40% vs. 22%, p = 0.018), whereas positive remodeling, volume of low attenuation plaque, and incidence of napkin-ring sign were not significantly different between the study groups or in ascending versus descending plaques. The volume of pericoronary fat around the plaque was significantly larger near eccentric lesions (707.68 ± 454.08 mm3 vs. 483.25 ± 306.98 mm3, p = 0.046) and descendent plaques (778.26 ± 479.37 mm3 vs. 473.60 ± 285.27 mm3, p = 0.016). Compared to ascending lesions, descendent ones presented a significantly larger volume of thoracic fat (1,599.25 ± 589.12 mL vs. 1,240.71 ± 291.50 mL), while there was no significant correlation between thoracic fat and cross-sectional eccentricity. Conclusions: The phenotype of plaque distribution and geometry seems to be associated with a higher vulnerability of coronary lesions and may be influenced by the local accumulation of inflammatory mediators released by the pericoronary epicardial adipose tissue.

Vibration analysis of a rotating pre-twisted blade considering the coupling effects of stretching, bending, and torsion

An enhanced dynamic model for a rotating pre-twisted blade with arbitrary cross-section is proposed in this study. The coupling effects between stretching, bending, and torsion are considered simultaneously in this model. To derive the equations of motion, deformation variables, including a special variable representing stretch, are approximated using the assumed mode method. The stretch variable plays a key role in the coupling effects between stretching, bending, and torsion. The accuracy of the proposed model was validated by comparing the analysis results to those obtained using a commercial finite element code. The effects of several parameters, such as cross-section eccentricity, pre-twist angle, torsion to bending stiffness ratio, and angular speed, on the modal characteristics of the blade were investigated using the proposed model. It was found that coupled modal characteristics of a rotating pre-twisted blade could be accurately estimated with the proposed model.

A Lagrangian cylindrical coordinate system for characterizing dynamic surface geometry of tubular anatomic structures

Vascular morphology characterization is useful for disease diagnosis, risk stratification, treatment planning, and prediction of treatment durability. To quantify the dynamic surface geometry of tubular-shaped anatomic structures, we propose a simple, rigorous Lagrangian cylindrical coordinate system to monitor well-defined surface points. Specifically, the proposed system enables quantification of surface curvature and cross-sectional eccentricity. Using idealized software phantom examples, we validate the method’s ability to accurately quantify longitudinal and circumferential surface curvature, as well as eccentricity and orientation of eccentricity. We then apply the method to several medical imaging data sets of human vascular structures to exemplify the utility of this coordinate system for analyzing morphology and dynamic geometric changes in blood vessels throughout the body.Graphical abstractPointwise longitudinal curvature of a thoracic aortic endograft surface for systole and diastole, with their absolute difference.

Nonlinear galloping of internally resonant iced transmission lines considering eccentricity

Based on the curved-beam theory, a nonlinear galloping model considering three displacement (normal, bi-normal and tangential) components and twist is formulated. According to the property of transmission line, one reduced (normal and bi-normal) galloping model, with regard of bending, rotation and eccentricity of cross section, is obtained. Moreover, the initial rotation angle is also introduced in galloping and aerodynamic models. Additionally, based on the reduced model, the bifurcation and stability of the two cases (1:1 resonance and 2:1 resonance) are analyzed. The results turn out that the importance of ice eccentricity needs to be highlighted. Finally, multiple stabilities are found through the analyses of bifurcation and stability and proved by the reduced model and Reduced Amplitude Modulation Equations (RAME) numerically integrated in time history.

ACOUSTIC PROPAGATION IN DUCTS WITH SLOWLY VARYING ELLIPTIC CROSS-SECTION

The propagation of acoustic waves along a duct of elliptic cross-section, the eccentricity of which varies slowly along the axis, is considered as a model of the unsteady flow inside a realistic aeroengine nacelle. This is a development of recent work on a circular duct by Rienstra. The acoustic field at each axial location is expanded in terms of the local even and odd Mathieu modes, and the slow variation of the axial wavenumber and the modal amplitude along the duct are determined as part of the solution. The duct eccentricity is seen to have a very significant effect right across the range of practical azimuthal orders, and has different effects on the even and odd modes. For instance, the point at which a given mode changes from being cut-on to cut-off depends on the eccentricity; for even modes, and for the odd modes apart from at a very low frequency, the eccentricity makes modes more cut-on than in a circular duct. Even for cases in which a given mode is cut-on all along the duct according to standard circular duct theory, the modal amplitude is seen to depend strongly on the cross-sectional eccentricity. In a representative case the amplitude of a high order mode propagating upstream along a slowly varying elliptical duct is seen to be significantly lower than that of the equivalent mode propagating in a circular duct of the same cross-sectional area.

Ballistic transport in a quantum wire with a noncircular cross-section

The conductance quantization in a quantum wire with an elliptic cross-section is considered by means of the parabolic confining potential. The number of the conductance steps and the width of the conductance plateau is studied as a function of the cross-section eccentricity. The effect of temperature on the shape of the plateau and the thresholds of the steps is analysed.

A STUDY OF SPIRAL GRAIN IN CLONES OF P. RADIATA

SUMMARY Determinations of the angle of surface grain relative to the pith and relative to the central axis were made on discs cut from thinnings in two clonal stands, nine years old. Unexpected variation was observed within each clone and even within any one disc. Nevertheless significant differences in mean angle of slope were found between these clones, at all heights, and an increase of mean angle was noted proceeding up the stems. No relationship was observed between slope of grain and eccentricity of cross-section. Such relationship as was noticed between slope of grain and diameter at breast height may be attributable to differential height growth. It is recommended that spiral grain should be assessed from complementary determinations on any opposite radii.