Perforation Pattern Research Articles

Numerical Study of Circle Fractal Grid Perforated Plate as a Turbulent Generator in Combustion Chamber

Fractal grids can be used to design turbulent flows with low power losses and high turbulence intensities for intense yet economic mixing over a region of designed length and location. The introducing circle grid perforated plate is the main aim of this present paper. In this numerical work, we want to ascertain a new approach in turbulence generators on the structure of premixes flames using perforated plate fractal-grids pattern. In this paper, we compared circle grid perforated plate by varies using its diameters, spacing and number of holes on the plate. The result showed good perceptivity of the fractal generated turbulence and the fractal flow physics. The turbulent intensity can be increased by a grid with higher blockage ratio.

Lateral lower leg perforator flaps: an anatomical study to localize and classify lateral lower leg perforators.

Despite increasing use of lateral lower leg perforator flaps, comprehensive anatomical data are still lacking. The aim of this article was to comprehensively document the pattern of usable lateral lower leg perforators. Systematic mapping of 16 cadaver leg perforators in a well-defined area was performed to elucidate location, course, length, diameter, and origin. Overall, 197 perforators were found in 16 lateral lower legs. The mean number of perforators per leg with a diameter ≥ 0.3 mm was 13.4 ± 3.6. Most perforators were found in the distal third (39.0%), followed by the middle third (32.0%), and proximal third (29.0%). A musculocutaneous course was found in 26.9% of the perforators, whereas 73.1% revealed a septocutaneous course. Most septocutaneous perforators (50.0%) were found in the distal third and most musculocutaneous perforators (58.5%) in the proximal third (P < 0.001). The majority of perforators originated from the anterior tibial artery (53.0%), followed by the peroneal artery (41.6%), and the popliteal artery (5.1%). Popliteal artery perforators (1.64 mm) were significantly larger than anterior tibial artery (0.91 mm) and peroneal artery perforators (1.02 mm; P < 0.001). These results may facilitate tissue transfer around the lateral lower leg.

Time to appendectomy and risk of perforation in acute appendicitis.

In the traditional model of acute appendicitis, time is the major driver of disease progression; luminal obstruction leads inexorably to perforation without timely intervention. This perceived association has long guided clinical behavior related to the timing of appendectomy. To evaluate whether there is an association between time and perforation after patients present to the hospital. Using data from the Washington State Surgical Care and Outcomes Assessment Program (SCOAP), we evaluated patterns of perforation among patients (≥18 years) who underwent appendectomy from January 1, 2010, to December 31, 2011. Patients were treated at 52 diverse hospitals including urban tertiary centers, a university hospital, small community and rural hospitals, and hospitals within multi-institutional organizations. The main outcome of interest was perforation as diagnosed on final pathology reports. The main predictor of interest was elapsed time as measured between presentation to the hospital and operating room (OR) start time. The relationship between in-hospital time and perforation was adjusted for potential confounding using multivariate logistic regression. Additional predictors of interest included sex, age, number of comorbid conditions, race and/or ethnicity, insurance status, and hospital characteristics such as community type and appendectomy volume. A total of 9048 adults underwent appendectomy (15.8% perforated). Mean time from presentation to OR was the same (8.6 hours) for patients with perforated and nonperforated appendicitis. In multivariate analysis, increasing time to OR was not a predictor of perforation, either as a continuous variable (odds ratio = 1.0 [95% CI, 0.99-1.01]) or when considered as a categorical variable (patients ordered by elapsed time and divided into deciles). Factors associated with perforation were male sex, increasing age, 3 or more comorbid conditions, and lack of insurance. There was no association between perforation and in-hospital time prior to surgery among adults treated with appendectomy. These findings may reflect selection of those at higher risk of perforation for earlier intervention or the effect of antibiotics begun at diagnosis but they are also consistent with the hypothesis that perforation is most often a prehospital occurrence and/or not strictly a time-dependent phenomenon. These findings may also guide decisions regarding personnel and resource allocation when considering timing of nonelective appendectomy.

Prevalence, morbidity, and mortality patterns of typhoid ileal perforation as seen at the University of Nigeria Teaching Hospital Enugu Nigeria: an 8-year review.

BackgroundSome recent studies have reported a decrease in mortality from typhoid ileal perforation. The present report aims to determine the prevalence, morbidity, and mortality of this disease in patients mostly drawn from a rural area.MethodsThis is a retrospective study of 50 patients treated between January 1999 and December 2007 at the University of Nigeria Teaching Hospital, Enugu, Nigeria. The variables studied included patient demographics, clinical features, intraoperative findings, complications, and mortality. Statistical analysis was done with SPSS version 13.ResultsOf the 50 patients included in the study, 22 were males with the highest rate in patients aged 20 years and younger. Fever was the commonest symptom and at initial presentation, the mean pulse and respiratory rates were significantly higher in the patients who subsequently died than in those who survived (P < 0.05). All the perforations occurred in the ileum; 62 % of the patients had solitary perforations, 28 % had double perforations, and 10 % had three or more. Fifty-eight perforations were treated by simple closure in two layers, 4 patients had ileal resection and anastomosis, and 2 underwent right hemicolectomy. The mean interval between operation and death was 1.7 days. The overall mortality rate was 30 %, but among those with three or more perforations, mortality was 100 %.ConclusionsTyphoid ileal perforation still carries a high mortality especially in rural areas. Those with tachycardia and tachypnea at presentation and those with three or more perforations are at a higher risk of dying from the disease.

Flow rate — pressure head characteristics of a hydrodiode

Results of a study of the flow rate — pressure head characteristics of a perforated membrane immersed in an oscillating liquid flow are reported; such characteristics need to be known when hydropneumodiodes are used as a pump. We show that the perforation pattern (or, more specifically, the number of perforated holes) affects just the rate of the liquid flow through membrane.

Laser-Perforated Carbon Paper Electrodes for High-Power Vanadium Redox Flow Batteries

Recently, there has been considerable effort to increase the power density and lower the cost of vanadium flow battery (VRFB) systems via new system architectures and optimized electrode materials. To date, research on electrodes has primarily focused on improving the surface area, surface chemistry, pore size distribution and resistivity of the material to improve the reaction kinetics, mass transport ability and the areal series resistance (ASR).While carbon felt materials have been conventionally used, the recent push for higher power densities has required the application of new electrode materials.Carbon paper was proposed by Aaron et al. as high-performance VRFB electrode material [1]. This material has a reduced thickness and high active surface area, as compared to carbon felt, which reduces the ASR and overpotential, and significantly improves the current- and power density. In their study, the authors demonstrated a VRFB with a peak power of 557 mW cm-2 . Liu et al. further improved the performance of a VRFB with no-gap architecture by thermal pre-treatment of carbon paper electrodes in air [2]. The thermal treatment showed a 16% improvement in power density compared to the raw material.Although carbon paper electrodes exhibit significantly higher power density than carbon felt electrodes, they have a significantly lower porosity and reduced pore size. As a result, mass transport is expected to be problematic in these materials. To address these limitations, we utilized a procedure similar to Manahan et al. [3] by introducing laser perforations to facilitate the transport of reactants within this type of electrodes. A CO2 laser was employed to cut different hole patterns in SGL 10AA carbon paper. Specifically, the hole diameter and hole density (number of holes per electrode) were varied in order to better understand the tradeoffs between improved mass transport and reduced surface area in these materials. It was found that a 30% improvement in power density (as compared to non-perforated electrode) was achieved through optimization of the perforation pattern. Interestingly, this condition corresponds to a loss of 15% of the original surface area due to laser perforation. The results of this study highlight the fact that by proper tailoring the transport pathways in the electrode structure, it is possible to achieve significantly higher power density with a low surface area electrode material.

Branching Patterns Determine the Size of Single Subcortical Infarctions

The size variation of single subcortical infarcts (SSIs) may be because of differences in stroke mechanisms or branching patterns of perforators. We aim to investigate this issue using high-resolution MRI. Patients with high-resolution MRI-identified SSI without significant (≥50%) middle cerebral artery stenosis were enrolled. Perforator stems were defined as perforators originating from the middle cerebral artery and perforator branches as linear structures inside the infarcted area, traceable from >2 adjacent slices. The branching index was calculated as the number of perforator branches divided by the number of perforator stems. Clinical and imaging characteristics were compared between large (≥20 mm in diameter) and small SSI groups. Forty-one patients (10 large and 31 small SSIs) were enrolled. Larger SSIs were more closely associated with diabetes mellitus and severe neurological dysfunction but not with the presence of middle cerebral artery plaque. Although there was no difference in the number of perforator stems, the number of perforator branches (4.8±2.2 versus 2.3±1.4; P=0.005) and branching index (2.9±1.0 versus 1.2±0.8; P<0.001) was higher in the large SSI group. SSI diameter showed a significant correlation with the number of perforator branches (r=0.630; P<0.001) and branching index (r=0.750; P<0.001). SSI diameter seems to be associated with anatomic branching variation rather than the mechanism of stroke. Definition of small vessel disease with lesion diameter criteria may not be appropriate.

Finite strip elastic buckling solutions for thin-walled metal columns with perforation patterns

Approximate finite strip eigen-buckling solutions are introduced for local, distortional, flexural, and flexural-torsional elastic buckling of a thin-walled metal column with perforation patterns. These methods are developed to support a calculation-based strength prediction approach for steel pallet rack columns employing the American Iron and Steel Institute׳s Direct Strength Method, however they are generally posed and could also be useful in structural studies of thin-walled thermal or acoustical members made of steel, aluminum, or other metals. The critical elastic global buckling load including perforations is calculated by reducing the finite strip buckling load of the cross-section without perforations using the weighted average of the net and gross cross-sectional moment of inertia along the length of the member for flexural (Euler) buckling, and for flexural-torsional buckling, using the weighted average of both the torsional warping and St. Venant torsional constants. For local buckling, a Rayleigh–Ritz energy solution leads to a reduced thickness stiffened element equation that simulates the influence of decreased longitudinal and transverse plate bending stiffness caused by perforation patterns. The cross-section with these reduced thicknesses is input into a finite strip analysis program to calculate the critical elastic local buckling load. Local buckling at a perforation is also treated with a net section finite strip analysis. For distortional buckling, a reduced thickness equation is derived for the web of an open cross-section to simulate the reduction in its transverse bending stiffness caused by perforation patterns. The approximate elastic buckling methods are validated with a database of 1282 thin shell finite element eigen-buckling models considering five common pallet rack cross-sections featuring web perforations that include 36 perforation dimension combinations and twelve perforation spacing combinations.

The scars of time: the disappearance of peptic ulcer-related pyloric stenosis through the 20th century.

The changing pattern of haemorrhage and perforation from peptic ulcer disease is well documented but little is known about pyloric stenosis, the third complication of the disease. We reviewed records relating to definitive operations (with intent to cure) for peptic ulcer disease carried out in York, UK from 1929-1997. We categorised the patients as pyloric stenosis and no pyloric stenosis based on findings at operation and examined the change in total number of cases with pyloric stenosis and proportion of cases with pyloric stenosis, by year of operation and by decade of birth. To place our results in perspective, we reviewed world literature to examine rates of pyloric stenosis as a percentage of operative cases reported in other case series in the 20th century. 4178 patients were included in the analysis; 3697 without pyloric stenosis and 481 with pyloric stenosis (11.5%). Analysis by birth cohort showed that the proportion found to have pyloric stenosis at surgery fell from 17% in the first cohort (birth 1880-89) to only 2.9% in the last cohort (birth 1950-59; p<0.001). Mean age at operation fell more steeply for those with pyloric stenosis: 74 to 30 years vs. 65 to 28 years (p <0.001). The trend of final decline started before the introduction of modern medical treatment. Review of similar case series from across the world shows a similar decline in the proportion of peptic ulcer cases showing pyloric stenosis at operation. The reduction in pyloric stenosis over the last several decades is disproportionately greater than the change seen in peptic ulcer disease requiring surgery. Our findings suggest that this reduction in pyloric stenosis is largely the result of the changing natural history of the disease rather than due to the introduction of acid-suppressing medication.

Nonlinear seismic analysis of perforated steel plate shear walls

The behaviour of unstiffened steel plate shear walls with circular perforations in the infill plates is examined. A shear strength model of the infill plate with multiple circular openings is proposed based on a strip model. Eight perforation patterns in a single storey steel plate shear wall of two different aspect ratios were analyzed using a geometric and material non-linear finite element model to assess the proposed shear strength model. A comparison between the nonlinear pushover analysis and the proposed shear strength equation shows excellent agreement. The proposed model is used to design the boundary columns of three sample four-storey perforated shear walls. A comparison between the predicted design forces in the boundary columns for the selected shear walls with the forces obtained from nonlinear seismic analyses demonstrates the accuracy of the proposed simple model to predict the design forces in the columns.

Experimental study of perforated yielding shear panel device for passive energy dissipation

This paper describes an investigation into a metallic energy dissipater designed for earthquake risk mitigation of civil structures. It is called the Perforated Yielding Shear Panel Device (PYSPD). It comprises of a thin perforated diaphragm plate welded inside a short length square hollow section. The device is to be connected in the lateral load resisting system of a structure with the diaphragm plate being in the plane of the building frame. It is a displacement-based device in which energy is dissipated through plastic shear deformation of its perforated diaphragm plate. The PYSPD is a modified version of the previously tested Yielding Shear Panel Device (YSPD). Perforations on the diaphragm plate alleviate demand on supporting elements which reduces undesirable local deformations near the connections. As a result more stable force-displacement hysteresis is obtained. Three patterns of perforations are studied. Finite element models confirm that diagonal tension field develops under shearing action but stress patterns are affected by perforations. Two plate slenderness and three perforation patterns combinations were tested experimentally. Under quasi-static condition, devices with certain plate slenderness produced stable and repeatable force-displacement hysteresis, and achieved large energy dissipation capability. Compared to un-perforated specimens, perforations reduce elastic stiffness and yield strength. Under design displacement it produced a stable hysteretic behavior and endured code requirements against low-cycle fatigue.

Decoupling Diameter and Pitch in Silicon Nanowire Arrays Made by Metal‐Assisted Chemical Etching

The fabrication of well‐separated, narrow, and relatively smooth silicon nanowires with good periodicity is demonstrated, using non‐close‐packed arrays of nanospheres with precisely controlled diameters, pitch, and roughness. Controlled reactive ion etching in an inductively coupled plasma reduces the self‐assembled nanospheres to approximately a tenth of their original diameter, while retaining their surface smoothness and periodic placement. A titanium adhesion layer between the silicon substrate and gold film allows much thinner catalyst layers to be continuous, facilitating the film liftoff and formation of the perforated pattern without influencing catalyzed etching of silicon. Using these methods, a periodic array of silicon nanowires with a large pitch and small diameter (e.g., a 490 nm pitch and 55 nm diameter) is created, a combination not typically found in the open literature. This approach extends the types and quality of silicon nanostructures that can be fabricated using the combined nanosphere lithography and metal‐assisted chemical etching techniques.

Viscous damping and spring force calculation of regularly perforated MEMS microstructures in the Stokes’ approximation

There are a number of applications for microstructure devices consisting of a regular pattern of perforations, and many of these utilize fluid damping. For the analysis of viscous damping and for calculating the spring force in some cases, it is possible to take advantage of the regular hole pattern by assuming periodicity. Here a model is developed to determine these quantities based on the solution of the Stokes’ equations for the air flow. Viscous damping is directly related to thermal–mechanical noise. As a result, the design of perforated microstructures with minimal viscous damping is of real practical importance. A method is developed to calculate the damping coefficient in microstructures with periodic perforations. The result can be used to minimize squeeze film damping. Since micromachined devices have finite dimensions, the periodic model for the perforated microstructure has to be associated with the calculation of some frame (edge) corrections. Analysis of the edge corrections has also been performed. Results from analytical formulas and numerical simulations match very well with published measured data.

Computational impact responses of reinforced concrete slabs

The responses of reinforced concrete slabs subject to an impact loading near the ultimate load range are explored. The analysis is carried out on a simply supported rectangular reinforced concrete slab using a nonlinear explicit dynamic procedure and considering three material models: Drucker-Prager, modified Drucker-Prager, and concrete damaged plasticity, available in the commercial finite element software, ABAQUS/Explicit. For comparison purposes, the impact force-time response, steel reinforcement failure, and concrete perforation pattern are verified against the existing experimental results. Also, the effectiveness of mesh density and damage wave propagation are studied independently. It is shown that the presently adopted finite element procedure is able to simulate and predict fairly accurate the behavior of reinforced concrete slab under impact load. More detailed investigations are however demanded for the justification of effects coming from an imperfect projectile orientation as well as the load and structural surface conditions, including the impulsive contacted state, which are inevitable in an actual impact environment.

Determination of the Fundamental Frequency of Perforated Rectangular Plates: Concentrated Negative Mass Approach for the Perforation

This paper is concerned with a vibration analysis of perforated rectangular plates with rectangular perforation pattern of circular holes. The study is particularly useful in the understanding of the vibration of sound absorbing screens, head plates, end covers, or supports for tube bundles typically including tube sheets and support plates used in the mechanical devices. An energy method is developed to obtain analytical frequencies of the perforated plates with clamped edge, support conditions. Perforated plate is considered as plate with uniformly distributed mass. Holes are considered as concentrated negative masses. The analytical procedure using the Galerkin method is adopted. The deflected surface of the plate is approximated by the cosine series which satisfies the boundary conditions. Finite element method (FEM) results have been used to illustrate the validity of the analytical model. The comparisons show that the analytical model predicts natural frequencies reasonably well for holes of small size.

Sand Prediction: A Practical Finite-Element 3D Approach for Real Field Applications

Summary Sand production is a critical issue in the oil and gas industry. During the production of a well, sand production may have negative consequences, such as risk of well failure, erosion of pipelines and surface facilities, and the need for sand separation and disposal. Knowing the conditions for the onset of sand production allows optimizing sand free production and, eventually, avoiding or delaying the use of sand-control methods. The aim of this work is to establish a reliable workflow for the estimation of the conditions for sand production in real field cases by means of finite-element modeling. The fundamental requirement is to set up a 3D coupled model that can be easily adjusted to the most complex conditions (e.g., stress anisotropy, deviated wells, and complex perforation patterns). The most suitable geometries and associated meshing strategies to describe the wellbore, the perforation tunnels, and the surrounding formation are analyzed. Further improvements with respect to previous approaches include the fact that the drilling and completion phases were also simulated to compute the correct stress distribution before the production, and that fluid flow and rock deformation are simulated in a fully coupled way to investigate accurately the effect of drawdown. Shear failure of reservoir rock, considered as an elastoplastic medium, is the main sand-production mechanisms analyzed, and the damage of the rock around the perforations is evaluated by analyzing the distribution of the equivalent plastic strain. Two real field cases are simulated, and the results of the finite-element models are consistent with the ones obtained by means of an analytical models and with field observations. Moreover, this numerical approach allows quantifying the spatial distribution and the severity of the damage of the rock around the perforations, facts that are either oversimplified or not considered at all in analytical models. For future applications, this model can be straightforwardly extended to more complex conditions and can also be improved to provide volumetric sand prediction.

An Analytical Model to Determine Fundamental Frequency of Free Vibration of Perforated Plate by Using Greatest Integer Functions to Express Non Homogeneity

This paper aims at determining the fundamental frequency of square perforated plate with square perforation pattern of square holes. Rayleigh’s method is used for the solution of this problem. Non homogeneity in Young’s modulus and density at the perforation is expressed by using greatest integer function i.e. floor function. Boundary condition considered is clamped on all edges. Perforated plate is considered as plate with uniformly distributed mass and holes are considered as non homogeneous patches. The deflected surface of the plate is approximated by a function which satisfies the boundary conditions. Finite Element Method (FEM) modal analysis is carried out to validate the results of the proposed approach.

Microvascular reconstruction of the mandible: An argument for the fibula osteocutaneous free flap

Introduction/objectiveThe fibula osteocutaneous free flap has been a workhorse for mandibular reconstruction since Hidalgo's original description for its use for this purpose. The objective of this manuscript is to review the use of the fibula flap in mandibular reconstruction and to answer some of the commonly held misconceptions as to why some surgeons view it as an inferior reconstructive option to the vascularized iliac crest flap. Materials/methodsReview of the literature as it relates to the use of the fibula free flap in mandibular reconstruction and the senior author's experience. ResultsThe bicortical nature of the fibula provides a stable platform for endosseous implant placement, thus allowing for comprehensive oral rehabilitation and improving the quality of life in reconstructed patients. The fibula osteocutaneous free flap, however, is the longest vascularized bone flap available, allowing for reconstruction of the entire mandible. Given these attributes, it would seem unlikely that doubts regarding the adequacy of the fibula free flap in mandibular reconstruction exists. However, the principal arguments challenging the use of the fibula osteocutaneous free flap are the lack of height of the reconstructed fibula compared to the native mandible, unreliable skin perforators to support a skin paddle, insufficient soft tissue coverage, and the presence of vascular anomalies which may preclude its use. These presumed shortcomings are circumvented with various proven techniques to increase fibular height and anatomic studies demonstrating the cutaneous perforator patterns. ConclusionsWith these simple solutions in mind, the fibula osteocutaneous free flap will likely remain a workhorse for mandibular reconstruction, allowing for the reconstruction of virtually any oromandibular defect. It allows for both aesthetic, as well as, functional reconstruction of the mandible.

Guiding Local Perforator Flaps with Preoperative Imaging

Perforator flap nomenclature continues to evolve, with many classification schemes reported. Each of them focuses on the fascial penetration pattern of perforators, which has no impact on flap perfusion. With the advent of advanced imaging technologies, the subcutaneous course of perforators can be highlighted for the first time, offering new insight into flap design. The current study presents the authors' technique for imaging local perforator flaps with computed tomographic angiography, utilizing a standard technique for perforator imaging with computed tomographic angiogram, regardless of whether the flap is a local or free flap, and regardless of body region. This technique has been used in more than 1000 image-guided perforator flaps, with the current study highlighting three such cases in different body regions. With the use of preoperative imaging, flap design can be based on the subcutaneous ramification of individual perforators. Several ramification patterns are presented and potential improvements to nomenclature schemes suggested. : With the use of preoperative imaging, "image-guided" perforator flaps that are truly axial-pattern in terms of their arterial supply can be designed. Diagnostic: V.

Predicting results of DIEP flap reconstruction: The flap viability index

Worldwide experience with the DIEP flap has established its pre-eminent role in breast reconstruction after mastectomy. CT angiographic vascular imaging has enhanced the planning of reconstruction, allowing mapping of perforator patterns to increase the predictability of surgery. This study extends the role of perforator mapping, using measurement of perforator lumen diameters and flap weights to calculate an index that reliably predicts the amount of tissue which will survive. We call this the Flap Viability Index.