Circular Discontinuities Research Articles

Structural characterization of four different naturally occurring porcine collagen membranes suitable for medical applications.

Collagen is the main structural element of connective tissues, and its favorable properties make it an ideal biomaterial for regenerative medicine. In dental medicine, collagen barrier membranes fabricated from naturally occurring tissues are used for guided bone regeneration. Since the morphological characteristics of collagen membranes play a crucial role in their mechanical properties and affect the cellular behavior at the defect site, in-depth knowledge of the structure is key. As a base for the development of novel collagen membranes, an extensive morphological analysis of four porcine membranes, including centrum tendineum, pericardium, plica venae cavae and small intestinal submucosa, was performed. Native membranes were analyzed in terms of their thickness. Second harmonic generation and two-photon excitation microscopy of the native membranes showed the 3D architecture of the collagen and elastic fibers, as well as a volumetric index of these two membrane components. The surface morphology, fiber arrangement, collagen fibril diameter and D-periodicity of decellularized membranes were investigated by scanning electron microscopy. All the membrane types showed significant differences in thickness. In general, undulating collagen fibers were arranged in stacked layers, which were parallel to the membrane surface. Multiphoton microscopy revealed a conspicuous superficial elastic fiber network, while the elastin content in deeper layers varied. The elastin/collagen volumetric index was very similar in the investigated membranes and indicated that the collagen content was clearly higher than the elastin content. The surface of both the pericardium and plica venae cavae and the cranial surface of the centrum tendineum revealed a smooth, tightly arranged and crumpled morphology. On the caudal face of the centrum tendineum, a compact collagen arrangement was interrupted by clusters of circular discontinuities. In contrast, both surfaces of the small intestinal submucosa were fibrous, fuzzy and irregular. All the membranes consisted of largely uniform fibrils displaying the characteristic D-banding. This study reveals similarities and relevant differences among the investigated porcine membranes, suggesting that each membrane represents a unique biomaterial suitable for specific applications.

Reduction of systematic errors in structured light metrology at discontinuities in surface reflectivity

In measuring 3D shape with structured light techniques, systematic errors arise in the neighbourhood of discontinuities in reflectivity or geometry. A mechanism for this phenomenon is proposed, based on the finite size of the imaging system's point spread function. A theoretical analysis for the phase errors in a phase-shifting projected fringe system is given, from which a correction algorithm to minimise the systematic errors is presented. In this algorithm, a closed form expression for the errors based on the intensity values and the phase values in a neighbourhood excluding the affected region is used to remove the estimated error from the measured phase values within the affected region. Experiments on samples with both linear and circular discontinuities in reflectivity demonstrated respective reductions in systematic errors by factors of 2.5× and 3×.

Analysis of Spur Gear with Tooth Circular Discontinuity for Weight Reduction

The design of gears and gear drives are becoming challenging in automobile applications in which low contact ratio gears are required to transmit higher loads and be lighter in weight. There are various methods available for optimizing the design. Some researches have been taken place in the areas of gear tooth profile modifications for providing internal stress relief and weight reduction. In most cases, the maximum loads are assumed to be acting on the tip of the tooth. In this study, investigations are carried out on the effect of circular discontinuity on the weight reduction without affecting the root stress. The maximum tangential load is applied on the highest point of single tooth contact. The results show that with the modified gear tooth having a combination of two circular discontinuities of size 0.4 times the module not only provides weight reduction but also gives stress relief at the root.

Experimental Investigations on the Folding Process of Polyurethane Foam-Filled Aluminium Columns with Circular Discontinuities

This article performs an experimental study on empty and polyurethane foam-filled thin-walled aluminium columns with quadrangular cross section in two different conditions: with or without centrally circular discontinuities on the longitudinal or latitudinal sides of column cross section during the folding process (local buckling). In each sample, two circular cut-outs were perforated into the opposite sides of specimens and the samples were axially compressed between two rigid platens under the quasi-static loading. The samples were prepared with different initial lengths, filling conditions and cut-out diameters. Effects of mentioned characteristics are investigated on total absorbed energy, specific absorbed energy, crush force efficiency, peak load and folding wavelength. Experimental observations show that by increasing the cut-out diameter and also by filling the column with the foam, folding wavelength decreases. Also, experiments show that there is an optimum diameter for the longitudinal side cut-outs which total absorbed energy by the filled rectangular specimen with the optimum cut-out is the highest. Furthermore, results illustrate that total absorbed energy increases due to increment of column length, but specific absorbed energy and crush force efficiency are independent of column length.

Evaluation of energy absorption performance of steel square profiles with circular discontinuities

This article details the experimental and numerical results on the energy absorption performance of square tubular profile with circular discontinuities drilled at lengthwise in the structure. A straight profile pattern was utilized to compare the absorption of energy between the ones with discontinuities under quasi-static loads. The collapse mode and energy absorption conditions were modified by circular holes. The holes were drilled symmetrically in two walls and located in three different positions along of profile length. The results showed a better performance on energy absorption for the circular discontinuities located in middle height. With respect to a profile without holes, a maximum increase of 7% in energy absorption capacity was obtained experimentally. Also, the numerical simulation confirmed that the implementation of circular discontinuities can reduce the peak load (Pmax) by 10%. A present analysis has been conducted to compare numerical results obtained by means of the finite element method with the experimental data captured by using the testing machine. Finally the discrete model of the tube with and without geometrical discontinuities presents very good agreements with the experimental results.

Rigorous Characterization of Carbon Nanotube Complex Permittivity Over a Broadband of RF Frequencies

This study presents a comprehensive characterization of the frequency dependence of the effective complex permittivity of bundled carbon nanotubes (CNTs) considering different densities over a broadband of frequencies from 10 MHz to 50 GHz using only one measurement setup. The extraction technique is based on rigorous modeling of coaxial and circular discontinuities using a mode matching technique in conjunction with an inverse optimization method to map the simulated scattering parameters to those measured by a vector network analyzer. The dramatic values of complex permittivity obtained at low frequencies are physically explained by the percolation theory. The effective permittivity of a mixture of nanoparticles of alumina and CNTs versus frequency and packing density is studied to verify the previously obtained phenomenon.

Mode matching technique-based modeling of coaxial and circular waveguide discontinuities for material characterization purposes

In this paper, it is proposed to use a cylindrical cell for the characterization of dielectric material. The extraction of complex permittivity is based on inverse gradient approach where the full-wave simulation results are mapped to experimental data to extract the complex permittivity. As the operational frequency of radio frequency (RF)/microwave devices is increased, it becomes difficult to accurately model waveguide transitions using traditional methods based on meshing such as finite-element method (FEM) where mesh size is determined according to the wavelength. Moreover, these techniques usually require extensive computational resources. Mode matching technique (MMT) is the full-wave tool implemented in this current work. It is used to compute the generalized scattering matrices (GSMs) of the different discontinuities of test setup. These GSMs model precisely discontinuities as they include the effects of all higher-order modes propagating and evanescent. Simulation and experimental results are included to validate the proposed approach for the rigorous modeling of those discontinuities and hence the extraction of complex permittivity.

Automatic detection and sizing of pores from radiographic images using the Hough transform

We use a pattern recognition approach to assist the human interpreter in evaluating the quality of welds from radiographic images, especially tube-to-tubesheet weld joints in the steam generator assembly of the prototype fast breeder reactor (PFBR), that require stringent inspection as the joints separate water and steam. In this paper, the circular Hough transform is used for automatic detection of circular discontinuities that are present in the weld joints, and we use morphological parameters to classify these defects in terms of their size. Using this approach, a success rate of 99% detection of circular discontinuities is achieved, by segmenting the image into smaller regions of interest and using the circular Hough transform along with morphological parameters.

Experimentally Observed Strain Distributions Near Circular Discontinuities of AA6061-T6 Extrusions During Axial Crush

An experimental investigation to determine the strain distribution and collapse behaviour for AA6061-T6 square cross-sectional extrusions with and without circular discontinuities under quasi-static axial compressive loading was completed. Three-dimensional digital image correlation (DIC) was utilized for strain assessment. In order to validate the results of the optical strain measurement system, tensile tests were first conducted employing both the DIC technique and a traditional extensometer. Strain observations from both methods were found to be very consistent prior to strain localization in the test specimen. Quasi-static axial crushing tests were then conducted. Extrusions considered for the present research had a nominal side width, wall thickness and length of 38.1 mm, 3.15 mm, and 200 mm, respectively. A centrally-located circular hole with diameter of either 14.29 mm, 10.72 mm or 7.14 mm was incorporated into the extrusion. Square tubes without any discontinuities were also considered in the experimental testing program. Testing results showed that the collapse mode of the extrusion altered from global bending to a cutting and splitting deformation mode with the presence of the circular discontinuity. Strain localization occurred near the vicinity of the holes for all specimens. For discontinuities sized 14.29 mm and 10.72 mm the location of strain localization and the initiation of material fracture was at the edge of the discontinuity while the location for extrusions with a 7.14 mm hole was found to occur at the intersection of the extrusion side walls. Maximum values of the effective strain were found to vary from approximately 60% to 100%. The region of strain localization was consistent with the location where material fracture initiated.

The effect of the implementation of circular holes as crush initiators to the crushing characteristics of mild steel square tubes: experimental and numerical simulation

During a crash event, significant energy must be absorbed by kinetic energy-dissipating systems through material plastic deformation. Such systems are thin-walled steel tubes installed in specific places of the vehicle body to reduce the amount of forces transferred to occupants to a required safety limit and to minimise the cargo damage. The present paper deals with the improvement of the response characteristics of structural components by embodying geometrical discontinuities in the form of circular holes. These discontinuities play the role of crash initiators, which can affect the axial collapse mode, by ensuring a stable collapse process and decreasing the initial peak load. Results of both experimental and finite element (FE) simulation of square steel tubes with circular discontinuities subjected to quasi-static axial loadings are reported. The tubular test specimens were manufactured from commercially mild steel S355 tubes and were tested under various schemes of discontinuities (hole diameter, location, etc.). The proposed numerical model using the LS-DYNA explicit FE code was validated employing testing results from the axial loading and was found to be in good agreement with the experimental data.

Circular discontinuities detection in welded joints using Circular Hough Transform

Conventional radiography is one of the common non-destructive testing which employs manual image interpretation. The interpretation is very subjective and depends much on the inspector experience and working conditions. It is therefore useful to have pattern recognition system in order to assist human interpreter in evaluating the quality of the radiographed sample, especially radiographic image of welded joint. This paper describes a system to detect circular discontinuities that are present in the joints. The system utilizes together two different algorithms, which are separability filter to identify the best object candidate and Circular Hough Transform to detect the presence of circular shape. The result of the experiment shows a promising output in recognition of circular discontinuities in a radiographic image. This is based on 81.82–100% of radiography film with successful circular detection by using template movement of 10 pixels.

Experimental observations on the crush characteristics of AA6061 T4 and T6 structural square tubes with and without circular discontinuities

Quasi-static compressive testing of extruded aluminum alloy 6061-T4 and 6061-T6 square cross-sectional tubular specimens, with and without the presence of dual centrally located circular hole discontinuities, was completed to investigate the load management and energy absorption characteristics of these structural members. The tubular geometries selected (tube lengths of 200 mm and 300 mm, wall thickness of 3.15 mm, and nominal side width of 38.1 mm) had parameters which result in predicted global bending collapse under compressive loading. Centrally located circular holes, machined into the two opposing walls of the tubes, were used as crush initiators to commence the plastic buckling process. Holes with diameters of 7.1 mm and 14.2 mm were considered. In addition to progressive buckling, collapse modes involving cracking and splitting were observed in many tests and are characterized using photographs of the experimental process. The collapse modes and energy absorption of the crush test specimens were found to be dependent largely on material properties and to a lesser extent on the diameter of the discontinuity. Significant increases in the crush force efficiency, up to a maximum of approximately 22%, were observed for the shorter length tube geometry. However, the presence of the circular discontinuity within the AA6061 T4 300 mm tubes slightly degraded the crush force efficiency compared to the same length tubular member without any discontinuity. Energy absorption capabilities were substantially improved for all AA6061- T6 specimens containing a circular discontinuity relative to the specimens without any crush initiators. With the addition of the discontinuity, energy absorption was improved for the 200 mm length AA6061-T4 specimens but slightly decreased for the 300 mm length members.

Experimental observations on the crush characteristics of AA6061 T4 and T6 structural square tubes with and without circular discontinuities

Abstract Quasi-static compressive testing of extruded aluminum alloy 6061-T4 and 6061-T6 square cross-sectional tubular specimens, with and without the presence of dual centrally located circular hole discontinuities, was completed to investigate the load management and energy absorption characteristics of these structural members. The tubular geometries selected (tube lengths of 200 mm and 300 mm, wall thickness of 3.15 mm, and nominal side width of 38.1 mm) had parameters which result in predicted global bending collapse under compressive loading. Centrally located circular holes, machined into the two opposing walls of the tubes, were used as crush initiators to commence the plastic buckling process. Holes with diameters of 7.1 mm and 14.2 mm were considered. In addition to progressive buckling, collapse modes involving cracking and splitting were observed in many tests and are characterized using photographs of the experimental process. The collapse modes and energy absorption of the crush test specimens were found to be dependent largely on material properties and to a lesser extent on the diameter of the discontinuity. Significant increases in the crush force efficiency, up to a maximum of approximately 22%, were observed for the shorter length tube geometry. However, the presence of the circular discontinuity within the AA6061 T4 300 mm tubes slightly degraded the crush force efficiency compared to the same length tubular member without any discontinuity. Energy absorption capabilities were substantially improved for all AA6061- T6 specimens containing a circular discontinuity relative to the specimens without any crush initiators. With the addition of the discontinuity, energy absorption was improved for the 200 mm length AA6061-T4 specimens but slightly decreased for the 300 mm length members.

Systematic elaboration of trial function bases for the study of ridged circular waveguide discontinuities polarizer

AbstractThis paper presents a mixed method for the characterization of ridged circular waveguide discontinuities. The method is based on integral equations in combination with a scalar Green's function and a boundary element method for the calculation an arbitrary ridged circular waveguide's mode spectrum. The modes computed by this technique are used as trial function bases for the characterization of arbitrary ridged circular waveguide discontinuities. An improved variational multimodal formulation is used for the characterization of the step discontinuity. Coupling coefficients are evaluated by post processing of the matrices already used in the modes' determination, and the overall scattering matrix is obtained by cascading the impedance matrix of such a discontinuity. In order to validate this method, screws used in filter design and spectrum polarizer are modeled and the numerical results are verified by excellent agreement with published data. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 478–482, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10643

Stereological relationship between trace length and size distribution of elliptical discontinuities

This paper presents an approach for estimating the size distributions of elliptical discontinuities. This is an extension of approaches for estimating size distributions of circular discontinuities. By assuming an elliptical shape and changing the aspect ratio k of the ellipses (i.e. the ratio of the major to minor axes), many real discontinuities can be reasonably represented. For elliptical discontinuities, a general stereological relationship between distributions of trace length and distributions of discontinuity size (expressed by the major axis length, a, of the ellipse) is derived for area (or window) sampling. From this relationship, expressions are derived between the mean (μa) and standard deviation (σa) of the discontinuity size, a, and the mean (μl) and standard deviation (σl) of the trace length, l, respectively for log-normal, negative exponential and gamma distributions of discontinuity sizes. Using the derived expressions, the effect of sampling plane orientation on trace lengths is investigated. The results show that the sampling plane orientation has an important effect on both the mean and the standard deviation of trace lengths. Finally, the derived stereological relationship between the trace length distribution and the discontinuity size distribution was used in a simulation with the FracMan discrete fracture code. The results show that the approach for inferring the major axis orientation, aspect ratio and size distribution of discontinuities from observations on outcrops is satisfactory.

Stereological relationship between trace length and size distribution of elliptical discontinuities

This paper presents an approach for estimating the size distributions of elliptical discontinuities. This is an extension of approaches for estimating size distributions of circular discontinuities. By assuming an elliptical shape and changing the aspect ratio k of the ellipses (i.e. the ratio of the major to minor axes), many real discontinuities can be reasonably represented. For elliptical discontinuities, a general stereological relationship between distributions of trace length and distributions of discontinuity size (expressed by the major axis length, a, of the ellipse) is derived for area (or window) sampling. From this relationship, expressions are derived between the mean (μa) and standard deviation (σa) of the discontinuity size, a, and the mean (μl) and standard deviation (σl) of the trace length, l, respectively for log-normal, negative exponential and gamma distributions of discontinuity sizes. Using the derived expressions, the effect of sampling plane orientation on trace lengths is investigated. The results show that the sampling plane orientation has an important effect on both the mean and the standard deviation of trace lengths. Finally, the derived stereological relationship between the trace length distribution and the discontinuity size distribution was used in a simulation with the FracMan discrete fracture code. The results show that the approach for inferring the major axis orientation, aspect ratio and size distribution of discontinuities from observations on outcrops is satisfactory.

A mode-matching technique for the study of circular and coaxial waveguide discontinuities based on closed-form coupling integrals

A mode-matching scheme for the analysis of concentric circular and/or coaxial waveguide step discontinuities is proposed in this paper. An analytical evaluation of the involved coupling integrals for all possible discontinuities formed by any combination of a circular and a coaxial waveguide is performed. The originality mainly concerns the multimode excitation and scattering at a circular-to-coaxial waveguide step junction. Numerical results for a number of applications are compared against those of other techniques and/or measurements and are found to be in good agreement.

Purification of intact nuclear lamina and identification of novel laminlike proteins in Raji, a cell line devoid of lamins A and C

Research on the structure of the nuclear lamina and the nuclear matrix of cells devoid of lamins A and C has been hampered by the fact that intact residual nuclear structures are difficult to isolate from such cells. In this paper, we show that some extraction parameters, such as buffer composition and the nature of the detergent used to remove nuclear membranes, are critical for achieving isolation of whole nuclear residual structures from the lymphoblastic cell line Raji, used as a model for cells without lamins A and C. Electron microscopic analysis shows that the nuclear lamina of Raji cells is formed by a network of intermediate-size filaments interrupted with circular discontinuities. Both lamins B1 and B2, and lamin D/E, are present in this structure. In addition, a group of 45-kDa proteins or intermediate filament protein--reacting proteins (IFA-RPs), located uniquely in the lamina, were found to exhibit the same immunological and chemical characteristics as lamins. Although they behave like nuclear lamins, microsequencing analysis of the IFA-RPs has revealed no homology with known lamins. These IFA-RPs may contribute to the formation of the nuclear lamina filament network in the absence of lamins A and C.

Detection of spatial discontinuities in first-order optical flow fields

We investigated the extent to which the human visual system can detect discontinuities in first-order optical flow fields. We constructed two types of spatial discontinuities: a circular split field with a straight edge and a disk with annular surround. We used two different first-order optical flow components: an expansion and a rotation. We found an intriguing difference in the detection thresholds for straight and circular discontinuities. Whereas straight discontinuities yielded thresholds of 10%-50% difference in expansion or rotation, circular discontinuities could, at first, only be detected at extreme differences (>> 100%). After a learning period, thresholds for such stimuli decreased, but they remained significantly higher than thresholds for the straight edge. Thresholds rose for stimuli that formed a gradual transition between a circular and a straight edge, and they decreased with increasing eccentricity of the circular discontinuity. Results suggest that symmetry in this stimulus, defined by the coincidence of the center of expansion or rotation and the center of the circular discontinuity, was responsible for the difference in thresholds for circular and straight discontinuities.

Pressure Transient Behavior In Reservoirs With An Internal Circular Discontinuity

Abstract This paper presents the pressure transient response for reservoirs with an internal circular subregion. The solution is a generalization of that previously presented in the literature, which assumed that the subregion was either an impermeable barrier or a constant pressure circle. Two cases were considered, with the well located either inside or outside the circular discontinuity. When the well is located inside the circular subregion, the solution developed in the study is also a generalization of the well-known pressure response for a composite two-region system. The solution was obtained by using the concept of Green's function and by applying the Laplace transformation technique. The Laplace space response, although very complex, was inverted to real space with the Stehfest1 algorithm. When the well is located inside the circular subregion, the wellbore pressure response shows a behavior typical of radial composite systems, except for the effect of the well eccentricity, which acts as a skin factor. For the case where the active well is external to the subregion, three flow regimes are observed. The initial infinite-acting behavior and the late-time pseudoradial flow produce semilog straight lines which are parallel and reflect the transmissivity of the external region. The long-time effect of the discontinuity can be regarded as an apparent skin effect. The dependence of the solution on the diffusivity ratio, the mobility ratio, the geometric configuration and the size of the system was also investigated in the study. The solution can be used to simulate the pressure behavior for reservoirs which contain circular or approximately circular discontinuities, such as those caused by variations in rock and/or fluid properties due to the presence of shale lenses or fluid injection, for instance. The pressure solution can also be used to interpret single-well or interference tests in systems with these configurations.