Thin-walled Regions Research Articles

A Parameter to Identify Thin-walled Regions in Aneurysms by CFD

A Parameter to Identify Thin-walled Regions in Aneurysms by CFD

Clear Detection of Thin-Walled Regions in Unruptured Cerebral Aneurysms by Using Computational Fluid Dynamics

Thin-walled regions (TIWRs) within cerebral aneurysms have a high risk of rupture during surgical manipulation. Previous reports have demonstrated specific changes in the parameters of computational fluid dynamics in TIWRs; however, they have not been fully evaluated. We identified and investigated a novel parameter, wall shear stress vector cycle variation (WSSVV), with user-friendly software that could predict TIWRs. Twelve unruptured cerebral aneurysms were analyzed. TIWRs were defined as reddish areas compared with the normal-colored parent artery on intraoperative views. The position and orientation of these clinical images were adjusted to match the WSSVV color maps. TIWRs and thick-walled regions (TKWRs) were marked and compared with the corresponding regions on WSSVV maps. The default images obtained from WSSVV imaging required appropriate maximum color bar value (MCBV) adjustment for predicting TIWRs. Sensitivity and specificity analyses were performed by changing the MCBV from 300 to 700 at intervals of 100. With the optimal MCBV, the WSSVV values were quantitatively compared. All of the selected 18 TIWRs and 16 TKWRs corresponded to low- and high-value regions of the WSSVV color maps at the adjusted MCBV, respectively. The mean optimal MCBV was 483.3 ± 167.50 (range, 300-700). According to receiver operating characteristic analysis, the best MCBV for predicting TIWRs was 500 (highest sensitivity, 0.89; specificity, 0.94). Under this condition, the quantitative values of the computational fluid dynamics color maps for TIWRs and TKWRs were significantly different (P < 0.01). Low WSSVV values may indicate TIWRs within cerebral aneurysms.

Acoustic amplification utilizing stepped-thickness piezoelectric circular cylindrical shells

This paper presents a new approach to amplify the acoustic field generated by a uniform thickness piezoelectric cylindrical shell by introducing a stepped thickness variation at predetermined axial locations. The acoustic field and corresponding mode shapes of a uniform thickness piezoelectric tube are analyzed first and then, axial thickness variations are machined within the specified designed regions of the tube. The machining leads to the formation of thin-walled regions in the tube which localize the vibration amplitude within the machined spaces with higher amplitude. This results in a conspicuous increase of approximately 85% on average in the strength of the resultant acoustic field, though both specimens the uniform and stepped-thickness tubes have the same power consumption. The results of the simulations and experiments are in good agreement.

Computational Fluid Dynamic Analysis of Intracranial Aneurysms Using Newly Developed Software:Can It Predict the Thin-Walled Region of Intracranial Aneurysm Preoperatively?

Recent studies have shown that computational fluid dynamics(CFD)analysis is useful to evaluate flow dynamics of intracranial aneurysms. However, CFD analysis still requires high costs and substantial time even now. This study aimed to evaluate whether newly developed software can shorten the time for analysis and serve useful information during clipping surgery for intracranial aneurysms. CFD analysis was performed in 55 unruptured cerebral aneurysms in 51 patients. The time required for analysis of each aneurysm was recorded. On the basis of CFD analysis, both pressure and wall shear stress(WSS)were calculated as the values at the systolic and diastolic phases, and also the mean value through one cardiac cycle. These data were compared between thin-wall points and other points within each aneurysm. The average time required for analysis was 3 hours, ranging from 1 to 15 hours. The CFD data could be referenced during surgery in each patient. The pressure in about 93% and 80% of the thin-wall points was higher than that at other points within each aneurysm in the systolic and diastolic phases, respectively. However, there was no significant correlation between WSS and wall thickness in each aneurysm. This study clearly shows that newly-developed software is simple and requires much shorter time for CFD analysis than previous methods. Higher pressure through the cardiac cycle may efficiently predict a thin-wall region within intracranial aneurysms, which strongly suggests that CFD analysis would be a valuable tool to determine the treatment strategy in patients with unruptured aneurysms.

Effect of Die Lip Geometry on Polymer Extrudate Deformation in Complex Small Profile Extrusion

The extrusion of polymer profile products with complex microcross section is difficult due to the extrudate deformation, especially for the profile with multihollow lumens and inner ribs. In order to investigate the effect of die lip geometry on extrudate deformations, three-dimensional simulations have been undertaken for typical small profile extrusions both inside and outside the die using finite-element method (FEM). The Carreau model was used to describe the shear-thinning behavior of polymer melt. The systematic definitions of the die lip geometric parameters and evaluations of the extrudate deformations were proposed. It was found that the thickness and profile deformations happen asynchronously, and the existence of the inner rib changes the global deformation, which cannot be predicted by a deformation combination of the basic geometries. Among the investigated die lip geometric parameters, the wall thickness ratio has the most pronounced effect on both thickness and external profile deformations of the extrudates, with the maximum variation of more than 80%. The decrease of the hollow ratio significantly reduces the extrudate deformation extent, especially the extrudate external profile and the extrudate thickness of the thin-wall region. Even with uniform thickness, the location and shape of the inner rib also generate extrudate deformations not only on the inner rib but also on the thickness of the outer ring at the region not connected with it, by a minor variation level of 5–25%. Comprehensive understandings on the mechanism of extrudate deformations and effects of die lip geometry were obtained. Some hints for small profile die design were provided accordingly. Numerical results showed qualitative and quantitative agreement with the experiments.

Commentary&lt;subtitle&gt;Determining the Presence of Thin-Walled Regions at High-Pressure Areas in Unruptured Cerebral Aneurysms by Using Computational Fluid Dynamics&lt;/subtitle&gt;

Commentary&lt;subtitle&gt;Determining the Presence of Thin-Walled Regions at High-Pressure Areas in Unruptured Cerebral Aneurysms by Using Computational Fluid Dynamics&lt;/subtitle&gt;

Determining the Presence of Thin-Walled Regions at High-Pressure Areas in Unruptured Cerebral Aneurysms by Using Computational Fluid Dynamics.

Thin-walled regions (TWRs) of cerebral aneurysms are at high risk of rupture, and careful attention should be paid during surgical procedures. Despite this, an optimal imaging technique to estimate TWRs has not been established. Previously, pressure elevation at TWRs was reported with computational fluid dynamics (CFD) but not fully evaluated. To investigate the possibility of predicting aneurysmal TWRs at high-pressure areas with CFD. Fifty unruptured middle cerebral artery aneurysms were analyzed. Spatial and temporal maximum pressure (Pmax) areas were determined with a fluid-flow formula under pulsatile blood flow conditions. Intraoperatively, TWRs of aneurysm domes were identified as reddish areas relative to the healthy normal middle cerebral arteries; 5 neurosurgeons evaluated and divided these regions according to Pmax area and TWR correspondence. Pressure difference (PD) was defined as the degree of pressure elevation on the aneurysmal wall at Pmax and was calculated by subtracting the average pressure from the Pmax and dividing by the dynamic pressure at the aneurysm inlet side for normalization. In 41 of the 50 cases (82.0%), the Pmax areas and TWRs corresponded. PD values were significantly higher in the correspondence group than in the noncorrespondence group (P = .008). A receiver-operating characteristic curve demonstrated that PD accurately predicted TWRs at Pmax areas (area under the curve, 0.764; 95% confidence interval, 0.574-0.955; cutoff value, 0.607; sensitivity, 66.7%; specificity, 82.9%). A high PD may be a key parameter for predicting TWRs in unruptured cerebral aneurysms. CFD, computational fluid dynamicsMCA, middle cerebral arteryPave, average pressurePD, pressure differencePmax, maximum pressureTWR, thin-walled regionWSS, wall shear stress.

Elevated ventricular wall stress disrupts cardiomyocyte t-tubule structure and calcium homeostasis.

AimsInvaginations of the cellular membrane called t-tubules are essential for maintaining efficient excitation–contraction coupling in ventricular cardiomyocytes. Disruption of t-tubule structure during heart failure has been linked to dyssynchronous, slowed Ca2+ release and reduced power of the heartbeat. The underlying mechanism is, however, unknown. We presently investigated whether elevated ventricular wall stress triggers remodelling of t-tubule structure and function.Methods and resultsMRI and blood pressure measurements were employed to examine regional wall stress across the left ventricle of sham-operated and failing, post-infarction rat hearts. In failing hearts, elevated left ventricular diastolic pressure and ventricular dilation resulted in markedly increased wall stress, particularly in the thin-walled region proximal to the infarct. High wall stress in this proximal zone was associated with reduced expression of the dyadic anchor junctophilin-2 and disrupted cardiomyocyte t-tubular structure. Indeed, local wall stress measurements predicted t-tubule density across sham and failing hearts. Elevated wall stress and disrupted cardiomyocyte structure in the proximal zone were also associated with desynchronized Ca2+ release in cardiomyocytes and markedly reduced local contractility in vivo. A causative role of wall stress in promoting t-tubule remodelling was established by applying stretch to papillary muscles ex vivo under culture conditions. Loads comparable to wall stress levels observed in vivo in the proximal zone reduced expression of junctophilin-2 and promoted t-tubule loss.ConclusionElevated wall stress reduces junctophilin-2 expression and disrupts t-tubule integrity, Ca2+ release, and contractile function. These findings provide new insight into the role of wall stress in promoting heart failure progression.

Analysis feature recognition and mixed-dimensional model reconstruction from finite element analysis mesh model

Instead of extracting mid-surfaces from computer-aided design model, an automatic dimensional reduction approach is proposed, which simplifies the finite element analysis model into the mixed-dimensional model. The input finite element analysis model is first decomposed into a set of locally prominent cross-sections. Each prominent cross-section is digitalized as a d-dimensional point and clustered in the embedded space. By the clustered points, both long-slender and thin-wall regions are detected and recognized with the help of aspect ratio. Further the identified features are reduced into skeletons and mid-surfaces, respectively, and the elements of lower dimensionality are generated simultaneously. This dimensional reduction procedure is general and feasible. In this case, multi-resolution mesh models could be created without being transformed back into computer-aided design software, which is essential to the multi-disciplinary simulation. Finally, the simplification degree tests show that the nodes and elements are largely decreased; furthermore, the proposed approach is more effective than the traditional manual method on time consuming.

Functional Nerve-Vascular Reconstitution of the Bladder-Wall; Application of Patch Transplantation of Skeletal Muscle-Derived Multipotent Stem Cell Sheet-Pellets

A three-dimensional gel-patch-like nerve-vascular reconstitution system using the Skeletal Muscle-Derived Multipotent Stem Cell (Sk-MSC) sheet-pellet was applied to the reconstitution of the severely damaged bladder wall as a non-skeletal muscle tissue, but has high demand for function. The Sk-MSC sheet-pellet was prepared by the mild detachment of expanded/confluent cells in culture with EDTA, then, collected in a tube and centrifuged. The sheetpellet was pasted on the open thin-walled region of the damaged bladder wall made by myotomy (remove one-third of serosal smooth muscle layer associate with large disruptions of nerve-blood vessel networks retaining the mucosal layer). At 4 wk after transplantation, significant prevention of the reduction in the passive wall-tension, and the positive wall-contraction via electrical stimulation was observed in the transplanted group. Supporting these functional results, immunohistochemical and immunoelectron microscopic analysis revealed that the engrafted cells actively contributed to the reconstitution of blood vessels and peripheral nerves with differentiation into pericytes, endothelial cells, and Schwann cells. However, skeletal and smooth muscle formation was not observed. Thus, this method is potentially useful for the reconstitution of nerve-vascular networks in the bladder-wall to be retaining function such as passive tension and contractile function.

Comparison of standard endoscopic submucosal dissection (ESD) versus an optimized ESD technique for the colon: an animal study

Endoscopic submucosal dissection (ESD) is a promising therapeutic technique for en bloc resection of large gastrointestinal tumors. However, this technique has disadvantages such as a long intervention time, complexity of the procedure, and a higher rate of complications. The primary aims of the study were to show the feasibility of ESD in the pig colon and to evaluate a new ESD technique comprising the use of a newly developed hybrid knife for colon procedures combining RF (radiofrequency) application and a distance-dependent water-jet application. ESD was conducted at three different locations in the colon according to the computer-generated randomization list, using either the standard technique (injection needle, flex knife, and hook knife as therapeutic instruments and DRY CUT and SWIFT COAG as RF currents), or the new ESD technique (hybrid knife as the therapeutic instrument combined with the new cutting mode ENDO CUT D) in 12 healthy pigs. The perforation and bleeding rates were documented and statistically analyzed. Intervention time, resected specimen size, thermal and mechanical damage of the resection bed, and number of instrument changes required were also recorded. A total of 16 and 18 ESD procedures were performed by the standard and new techniques, respectively. Complete en bloc resection was achieved in all cases. The standard ESD technique showed a perforation rate of 25 % (4/16) whereas the new ESD technique resulted in a 5.5 % perforation rate (1/18) ( P = 0.035); bleeding rates were similar. The new ESD technique was significantly safer compared with the standard ESD technique. A new ESD technique for the successful en bloc resection in thin-walled regions such as pig colon has been described. This procedure is as effective as the standard procedure but is easier to handle and significantly safer.

Failure analysis of gray iron pump housings

Hydrostatic pressure testing of several large gray iron castings resulted in brittle overload failures. Subsequent failure analysis on two of the failed components revealed casting imperfections associated with the failure origins. In each case, the root cause of failure was related to the casting mold. The first incident involved an imperfection that resulted in a stress concentration that reduced the normally large critical flaw size to the microstructural level. A microstructural gradient adjacent to the fracture of the second casting was the result of an inadequate mold design that allowed for rapid cooling at a thin-walled region of the casting. Material selection was a concern of the manufacturer and was also investigated.

Laws of Incompressible-Fluid Turbulent Near-Wall Flows Following from the Limiting Asymptotic Properties

The averaged layered turbulent wall flows of an incompressible fluid are considered for an arbitrary wall roughness and a friction coefficient tending to zero. It is assumed that in the asymptotic limit the flow may be divided into two regions: an outer, only slightly disturbed region, and a thin wall region. A similarity law for the velocity disturbances in the outer region is established for cylindrical tubes with an arbitrary cross section. Using the asymptotically matched solutions in the inner and outer regions, the existence of a logarithmic velocity profile in the matching zone is proved. On the basis of a unique asymptotic approach, the existing semi-empirical solutions for tube flows are brought into consistency. A number of semi-empirical formulas for the velocity profiles, which refine and expand the range of applicability of existing relations, are proposed.

Tube morphology and activity patterns related to feeding and tube building in the polychaeteMesochaetopterus tayloriPotts

Tube morphology and activity patterns related to feeding and tube building in Mesochaetopterus taylori Potts were examined using entire specimens and tubes. Tube orientation in situ at Patricia Bay, Vancouver Island, British Columbia, Canada, was typically L-shaped, and tubes were buried to and rarely coursing deeper than 30 cm, with only 1–2 cm of tube aperture exposed at the sand surface. Perforations were found in a distinctive thin-walled region at the buried apex of the tube, and were absent in the much thicker remaining tube length. Filter feeding using one or two mucus bags was observed, while posteriorly directed peristalsis in the abdominal segments generated a current from the exposed tube opening towards the buried tube apex. Thermistor-probe recordings of laboratory-held specimens showed feeding activity to be most prevalent during the day, one mucus bag, on average, being produced every 5.5 min. Mucus bags were also utilized to transport sand during excavation. Tube construction was noted to take place at the buried end of the tube, where old perforations were covered over and new perforations made as the tube was extended. The production of one sand casting per hour was noted in worms undertaking tube construction in laboratory aquaria. Our findings are compared with data available on other members of the Chaetopteridae.

The Establishment and Structure of Latent Infections with Monilinia fructicola on Apricots

AbstractLatent infections of apricot fruit with Monilinia fructicola were initiated by inoculation at shuck fall and 43 and 63 days after shuck fall. The fungus entered via the stomata and penetrated a guard cell through the thin walled region at the stomatal pore. The fruit tissue responded by death of cells around the point of infection, suberization of walls of surrounding living cells and accumulation o phenolic compounds in cells up to 20 distant. Periderm developed around lesions formed at shuck fall but was absent from those formed 65 days later. When the fruit ripened, approximately 100 days after shuck fall, viable hyphae in latent infections escaped from the lesions by growing out between the cuticle and epidermis or just below the epidermal cells. Outbreak was more efficient from later inoculations and only a small proportion of latents initiated at shuck fall became invasive.

Living sieve cells of conifers as visualized by confocal, laser-scanning fluorescence microscopy

Confocal laser scanning microscopy (CLSM) and fluorochromes were used to visualize the assimilate-conducting sieve cells of conifers in vivo. When still nucleate, the cytoplasm of these cells shows streaming and occupies the cell periphery including the pitlike, thin wall regions where sieve areas would develop. During differentiation the nuclear fluorescence and the central vacuoles disappear. At maturity and after ER-specific staining the sieve areas are the most conspicuous character of sieve cells. Those linking two sieve cells are covered on either side with prominent amounts of ER, while those leading to a Strasburger (=albuminous) cell show fluorescence on the sieve-cell side only. Within the sieve-area wall fluorescence appears also in the common median cavity which is part of the symplastic path between sieve cells. Electron microscopy (EM) depicts the ER as complexes of densely convoluted tubules of smooth ER, equally on either side of a sieve area, provided that the fixation of this sensitive tissue is appropriate. Purposeful wounding causes a swelling and vesiculation of the ER-tubules which is visible in both CLSM and EM. Electron micrographs of ER-complexes at sieve areas -in this paper demonstrated in vivo -have often been argued to be artefacts, since they should raise flow resistance considerably and are not consistent with the Munch hypothesis on phloem transport. The implications of this location for phloem transport are discussed.

Investigation of laminar sublayer on permeable surfaces with injection

The thin-wall region — the laminar (or viscous) sublayer, in which the molecular mechanism of transfer predominates — plays an important role in friction and heat-transfer processes in a turbulent boundary layer. In particular, the relation between the sublayer thickness and the height of the surface roughness determines the nature of the flow — hydrodynamically smooth or rough — over the surface. This is of great practical importance and, hence, the roughness criterion has become the subject of numerous and systematic investigations. There are exhaustive data for the majority of the commonest cases encountered in practice [1]. The velocity on the boundary of the laminar sublayer appears as an important parameter in two-layer calculation schemes (e.g., [2–4], etc.). Although the theoretical analysis of a turbulent boundary layer with injection started several decades ago, there are at present hardly any reliable experimental data which can be used to determine the variation of the parameters within and at the boundary of the sublayer in relation to the injection rate. In this work we used interferometric diagnostics for precision experimental investigations of the parameters of the laminar sublayer on permeable surfaces with injection.

STRESSES AND STRAINS IN ADSORBENT–ADSORBATE SYSTEMS. II

It has been shown previously that when adsorbates act as single component complexes, i.e. behave as single substances in complex force fields, volumetric mean adsorbate and mean adsorbent stress intensities can be calculated from adsorption isotherm data. When potentials of surface regions in the micropore system of a porous adsorbent are statistically independent of pore structure, linear mean stress intensities of the solid are related to volumetric means through an equation containing a structure factor which is independent of the nature and pressure of the adsorbed gas.In this paper we present adsorption extension data for an active carbon rod when exposed to helium, hydrogen, nitrogen, argon, krypton, and water at pressures up to 1600 p.s.i. The data suggest that the potentials of the capillary regions are not independent of structure. An empirical correlation factor is introduced and the resulting semiempirical equation describes the data probably within the experimental error.The results suggest that in cases of moderately strong adsorption, adsorption potentials of thick-walled capillary regions are higher than those of thin-walled regions.