Axial Strips Research Articles

Surface Dielectric Barrier Discharge in a Cylindrical Configuration – Effect of Airflow Orientation to the Microdischarges

ABSTRACT This paper is devoted to studying the effect of airflow orientation on the microdischarges of the surface dielectric barrier discharge in cylindrical configuration through varying air input into the discharge chamber, the number of input nozzles, and the geometry of the active electrode. The air is supplied into the discharge chamber tangentially, radially, or axially through one or four input nozzles. Air input into the discharge chamber and the number of input nozzles determine the airflow regime. We used two active electrode geometries that are the axial strips or azimuthal rings. The change of active electrode geometry from rings to strips affects the orientation of microdischarges with respect to the airflow. For the discharge, the variation of air inputs and the number of input nozzles influences the flow regime in the discharge chamber, which, together with the active electrode geometry, affects the temperature field distribution in the chamber. These factors play an important role in plasmachemical processes leading to the discharge generation of various species, such as ozone. It is found that, for the maximum effect of airflow on discharge ozone generation, the streamlines should be uniformly distributed in the discharge chamber and predominantly oriented perpendicular to the majority of microdischarges.

Modelling non-symmetric collagen fibre dispersion in arterial walls.

New experimental results on collagen fibre dispersion in human arterial layers have shown that the dispersion in the tangential plane is more significant than that out of plane. A rotationally symmetric dispersion model is not able to capture this distinction. For this reason, we introduce a new non-symmetric dispersion model, based on the bivariate von Mises distribution, which is used to construct a new structure tensor. The latter is incorporated in a strain-energy function that accommodates both the mechanical and structural features of the material, extending our rotationally symmetric dispersion model (Gasser et al. 2006 J. R. Soc. Interface 3, 15-35. (doi:10.1098/rsif.2005.0073)). We provide specific ranges for the dispersion parameters and show how previous models can be deduced as special cases. We also provide explicit expressions for the stress and elasticity tensors in the Lagrangian description that are needed for a finite-element implementation. Material and structural parameters were obtained by fitting predictions of the model to experimental data obtained from human abdominal aortic adventitia. In a finite-element example, we analyse the influence of the fibre dispersion on the homogeneous biaxial mechanical response of aortic strips, and in a final example the non-homogeneous stress distribution is obtained for circumferential and axial strips under fixed extension. It has recently become apparent that this more general model is needed for describing the mechanical behaviour of a variety of fibrous tissues.

Residual Shear Deformations in the Coronary Artery

Quantifying arterial residual deformations is critical for understanding the stresses and strains within the arterial wall during physiological and pathophysiological conditions. This study presents novel findings on residual shear deformations in the left anterior descending coronary artery. Residual shear deformations are most evident when thin, long axial strips are cut from the artery. These strips deform into helical configurations when placed in isotonic solution. A residual shear angle is introduced as a parameter to quantify the residual shear deformations. Furthermore, a stress analysis is performed to study the effects of residual shear deformations on the intramural shear stress distribution of an artery subjected to pressure, axial stretch, and torsion using numerical simulation. The results from the stress analyses suggest that residual shear deformations can significantly modulate the intramural shear stress across the arterial wall.

A simple method for vital staining of elastin in arterial tissue.

Highly diluted solutions of Gentian Violet and Evans Blue were used to visualize the elastin network in viable porcine right common carotid artery (RCCA) preparations. The two simple, alternative methods of staining were applied to proximal, intermediate, and distal sections of RCCA under various experimental conditions. These included the state of the vessel wall soon after excision, under relaxed smooth muscle condition after preconditioning, and during vasoconstriction. Micrographs of arterial rings, sectors, and axial strips show that the RCCA is an artery of the elastic type at the proximal end and of the muscular type at the distal end. While in sections of freshly dissected or KCl-constricted arteries the elastic lamellae show the well-known waviness, those in sections from arteries with relaxed smooth muscle and after preconditioning appear nearly straight. It is hoped that the inexpensive staining tools will contribute to solve conflicting interpretations existing on elastin structures in the arterial wall.

Non-Euclidean Stress-Free Configuration of Arteries Accounting for Curl of Axial Strips Sectioned From Vessels

It is well known that arteries are subject to residual stress. In earlier studies, the residual stress in the arterial ring relieved by a radial cut was considered in stress analysis. However, it has been found that axial strips sectioned from arteries also curled into arcs, showing that the axial residual stresses were relieved from the arterial walls. The combined relief of circumferential and axial residual stresses must be considered to accurately analyze stress and strain distributions under physiological loading conditions. In the present study, a mathematical model of a stress-free configuration of artery was proposed using Riemannian geometry. Stress analysis for arterial walls under unloaded and physiologically loaded conditions was performed using exponential strain energy functions for porcine and human common carotid arteries. In the porcine artery, the circumferential stress distribution under physiological loading became uniform compared with that without axial residual strain, whereas a gradient of axial stress distribution increased through the wall thickness. This behavior showed almost the same pattern that was observed in a recent study in which approximate analysis accounting for circumferential and axial residual strains was performed, whereas the circumferential and axial stresses increased from the inner surface to the outer surface under a physiological condition in the human common carotid artery of a two-layer model based on data of other recent studies. In both analyses, Riemannian geometry was appropriate to define the stress-free configurations of the arterial walls with both circumferential and axial residual strains.

Dissection Properties and Mechanical Strength of Tissue Components in Human Carotid Bifurcations

Carotid artery dissections can be triggered by several factors. The underlying biomechanical phenomena and properties are unclear. This study investigates the dissection properties of 62 human carotid bifurcations using two experimental methods: direct tension and peeling tests. Direct tension tests study the mechanical strength of the tissue components in radial direction, while peeling tests quantify the fracture energy required to propagate a dissection in a tissue. Results show that the interface between the healthy adventitia and media has the highest radial failure stress (132±20kPa, mean±SD, n=25), whereas the lowest value occurs between the diseased intima and media (104±24kPa, n=18). The radial tissue strength at the bifurcation is the highest compared with locations that are away from the central region of the bifurcation. Force/width values required to separate the individual layers and to dissect the media in the circumferential direction are always lower than related values in the axial direction, suggesting anisotropic dissection properties. Dissection energies per reference area generated during the peeling tests are also lower for strips in the circumferential direction than for axial strips, and they vary significantly with the location, as shown for the media. Histological investigations demonstrate that interfacial ruptures mainly occur in the media in both types of tests and are 2-5 elastic lamellae away from the external and internal elastic laminae. A remarkably "rougher" dissection surface is generated during axial peeling tests when compared with tests performed in the circumferential direction.

Layer-Specific 3D Residual Deformations of Human Aortas with Non-Atherosclerotic Intimal Thickening

Data relating to residual deformations in human arteries are scarce. In this paper we investigate three-dimensional residual deformations for intact strips and for their separate layers from human aortas in their passive state. From 11 abdominal aortas with identified anamnesis, 16 pairs of rings and axial strips were harvested, and the rings cut open. After 16 h images of the resulting geometries were recorded, and the strips were separated into their three layers; after another 6 h images were again recorded. Image processing and analysis was then used to quantify residual stretches and curvatures. For each specimen histological analysis established that the intima, media and adventitia were clearly separated, and the separation was atraumatic. Axial in situ stretches were determined to be 1.196+/-0.084. On separation, the strips from the adventitia and media shortened (between 4.03 and 8.76% on average), while the intimal strips elongated on average by 3.84% (circumferential) and 4.28% (axial) relative to the associated intact strips. After separation, the adventitia from the ring sprang open by about 180 degrees on average, becoming flat, the intima opened only slightly, but the media sprang open by more than 180 degrees (as did the intact strip). The adventitia and intima from the axial strips remained flat, while the media (and the intact strip) bent away from the vessel axis. This study has shown that residual deformations are three dimensional and cannot be described by a single parameter such as 'the' opening angle. Their quantification and modeling therefore require consideration of both stretching and bending, which are highly layer-specific and axially dependent.

On the measurement of residual stress in plastic pipes

AbstractRecent work on the determination of residual stress in drawn pipes has revealed an error in previous methods used. Such pipes have residual stresses very different from those induced by melt extrusin during conventional pipe processing. In particular, it appears that there are considerable compressive stresses at the bore, and the hoop and axial values are not equal. In an attempt to measure these values, tests were performed on slit rings of varying length, and a pronounced dependence of ring overlap on length was observed. This was contrary to previous assumptions, and a corrected version of the analysis has been developed, which enables the true hoop and axial stresses to be determined by testing rings of various lengths. For isotropic pipes, it has been shown that hoop and axial stresses are roughly equal. Previous results obtained on thin pipe rings can now be corrected by multiplying by the factor 1/(1‐v). For anisotropic drawn pipes, a combination of rings and thin axial strips is used to determine the residual stresses. These pipes can show remarkably low stresses at the bore, which may play a significant part in determining their performance.

Hydrophobic strip-of-helix algorithm for selection of T cell-presented peptides

In extension of the hypothesis that an amphipathic alpha helix of I i (Phe 146−Val 164) bound to the foreign antigen-presenting site (desetope) of class II MHC molecules through hydrophobic amino acid residues (Phe 146, Leu 150, Leu 153, Met 157, Ile 160, Val 164) which were present in an axial strip along one side of the I i helix, we developed an algorithm to search for T cell-presented peptides showing a similar hydrophobic strip-of-helix. Such peptides might bind to the class II MHC molecule site which was complementary to the I i hydrophobic strip-of-helix. The strip-of-helix hydrophobicity index was the mean hydrophobicity (from Kyte-Doolittle values) of sets of amino acids in axial strips down sides of helices for 3–6 turns, at positions, n, n + 4, n + 7, n + 11, n + 14, and n + 18. Peptides correlating well with T cell responsiveness had: (1) 12–19 amino acids (3–5 cycles or 4–6 turns of an alpha helix), (2) a strip with highly hydrophobic residues, (3) adjacent, moderately hydrophilic strips, and (4) no prolines. The degree of hydrophilicity of the remainder of a putative antigenic helix above a threshold value did not count in this index. That is, the magnitude of amphipathicity was not judged to be the principal selecting factor for T cell-presented peptides. This simple algorithm to quantitate strip-of-helix hydrophobicity in a putative amphipathic alpha helix, allowing otherwise generally hydrophilic residues, predicted 10 of 12 T cell-presented peptides in seven well-studied proteins. The derivation and application of this algorithm were analyzed.

Damped Response of Shells by a Constrained Viscoelastic Layer

Vibration absorbers are introduced into an asymmetric configuration of thin cylinders and tori enclosing an acoustic medium. The absorbers consist of thin axial strips bonded to the cylinder with a thin viscoelastic layer. The constrained layer dissipates the energy of relative motions between strip and cylinder. The absorber is most effective on response modes with two or more circumferential waves. The use of transfer matrices is extended to the coupled cylinder-absorber system.

Design of Waveguide E-Plane Filters with All-Metal Inserts

Waveguide E-plane filters with all-metal inserts are designed by a procedure based on the reflection coefficients of axial inductive strips. The scattering matrix, representing the junction in a bifurcated waveguide, is calculated by a mode-matching method. The reflection coefficient for an inductive strip is then obtained by cascading two scattering matrices separated by a distance equal to the stripwidth. The design is valid up to moderate bandwidths, except for the narrowband design at the higher waveguide frequency range, where both the center frequency and the bandwidth are inaccurate. Possible sources of error are studied and a method minimizing the error is proposed.

Stress and buckling of nonuniformly heated cylindrical and conical shells.

A computer program for the stress and stability analysis of segmented, ring-stiffened shells of revolution is used to calculate thermal stress and buckling of nonuniformly heated monocoque cones and ring-stiffened cylinders. Comparisons between test and theory are given for stress and buckling of nonuniformly axially compressed and heated ring-stiffened cylinders and cylinders and cones heated along axial strips. Particular attention is given to the effect of boundary conditions on predicted stress and critical temperatures. It is found that predicted buckling temperatures are not sensitive to width of heated strip even for very narrow strips. However, agreement between test and theory improves as the heated strip becomes narrower, presumably because large imperfections are less likely to occur within the thermally stressed portions of the shells where buckling occurs.

Buckling of thin cylindrical shells heated along an axial strip

The results of buckling tests on circular cylinders heated uniformly along axial strips are presented and discussed. Calculations of critical temperature based upon the small-deflection theory for thin circular cylindrical shells are included and a comparison is made between theoretical and experimental results. Cylinders heated along axial strips of given widths have a theoretically predicted behaivor which corresponds reasonably well to the behavior obtained by experiment. Curves are included showing the variation of critical temperature with respect to heated axial-strip width.