Perforation Pattern Research Articles

Critical reassessment of putative Acheulean Porosphaera globularis beads

Excavations at Acheulean sites in northern Europe at the end of the 19th century have yielded fossil sponges belonging to the Late Cretaceous species Porosphaera globularis . The spherical morphology of these fossils, their small size, and the presence of a natural complete perforation in their center have led some archaeologists to interpret them as the oldest known beads. Others argue that the presence of these fossils at archaeological sites is due to natural processes. Re-examination of material collected during the 19th century has recently revived the bead interpretation. We tested the bead hypothesis by analyzing 13 samples of Porosphaera from nine sites in Britain and France. We conducted morphometric and microscopic analyses on specimens recovered from archaeological sites ( n = 349), a natural geological sample, which was collected directly from Cretaceous strata ( n = 352), and a sample from a Bronze Age burial ( n = 43). Reappraisal of contextual data shows that the association of these finds with Acheulean artifacts is uncertain. Our results show that archaeological specimens are significantly different in size and perforation pattern from those of the natural geological sample. This may be due to size-sorting caused by sedimentary processes, size-selection by Palaeolithic people or by 19th century collectors. Modifications of the fossils' natural shape were detected on a few specimens in the form of localized abrasions and microchipping along the hole margins. A single specimen displays a facet close to the hole produced by grinding. The surfaces of these features exhibit a hue lighter than that observed on the remainder of the specimens indicating that they may be recent in origin and due to post-excavation and preservation treatment. However, this seems contradicted, for some specimens from Bedford, by the fact that according to Smith, W.G. [1884. On a Palaeolithic floor at North-East London. Journal of the Anthropological Institute of Great Britain and Ireland 13, 357–384] the specimens bearing microchipping and abrasions were found by him and “not touched or manipulated by the workmen”. We conclude that new excavations of these sites, involving systematic screening of sediments, are needed in order to attempt to solve the Porosphaera “mystery”.

Titanium alloy lattice truss structures

A high-temperature forming and diffusion bonding method has been investigated for the fabrication of modified pyramidal lattice core sandwich structures from a titanium alloy. A periodic asymmetric hexagonal perforation pattern was cut into thin Ti–6Al–4V sheets which were then folded along node rows by a combination of partial low-temperature bending followed by simultaneous hot forming/diffusion bonding to form sandwich panel structures with core relative densities of 1.0–4.1%. The out-of-plane compression and in-plane longitudinal shear properties of these structures were measured and compared with analytical estimates. Premature panel failure by node shear-off fracture was observed during shear testing of some test structures. Node failures were also initiated at stress concentrations at the truss–facesheet interface. A liquid interface diffusion bonding approach has been investigated as a possible approach for reducing this stress concentration and increasing the truss–facesheet interfacial strength.

Thermo-acoustic behaviour of multiple flame burner decks: Transfer Function (de)composition

The thermo-acoustic behaviour of multiple premixed laminar flames is analysed. The idea is used to (de)compose the flame Transfer Function (TF) of composite multiple flame configurations to/from the TF of constituent sub-systems of the flame. The TF superposition approach is based on the additive nature of the flame heat release rate. It is shown that the cumulative (total) flame TF can be represented as a weighted sum of elemental TF’s of the flame sub-systems where the weighting factors are related to the thermal power of the particular flames. On the basis of this approach, the thermo-acoustic TF’s of the burner decks with regular round hole perforation are experimentally studied. It is found that, the perforation hole diameter and the perforation pattern porosity are the governing parameters of the constituent TF’s. For burner decks with square patterns of unisize round holes the TF was studied as a function of the hole diameter, inter-hole spacing and mean flow rate. The TF composed via the superposition of TF’s measured for unisize perforations gives a good indication of the TF of the composite (multi-size) pattern if the elemental (unisize) TF’s are measured for the burner deck with the same porosity as the composite one. Possible simplifications and extensions of the proposed TF (de)composition principle are discussed. The practical perspective of this research is to offer an opportunity for the design of burner deck patterns with desirable acoustic characteristics.

Development of a maskless electrochemical texturing method

A simple method is demonstrated for texturing metallic surfaces by electrochemical machining, termed ‘maskless electrochemical texturing’ (MECT). The method allows a single cathode tool, in which the texture is incorporated through a pattern of perforations, to be used for many texturing operations and avoids the need for masks to be applied to individual workpieces. It therefore has significant advantages over conventional methods of texturing by electrochemical machining. The method has been applied to low-carbon steel workpieces and features up to 50 μm in depth have been produced. Current efficiencies of more than 90% have been achieved, and the texturing time is short enough for application in an industrial context. The process has been characterised in terms of the effects of current pulse history and electrolyte flushing conditions on current efficiency, material removal rate and feature definition.

Determination of the Temperature Distribution The Perforated Fins Under Natural Convection

This work treats the problem of heat transfer for perforated fins under natural convection. The temperature distribution is examined for an array of rectangular fins (15 fins) with uniform cross-sectional area (100×270 mm) embedded with various vertical body perforations that extend through the fin thickness. The patterns of perforations include 18 circular perforations (holes). Experiments were carried out in an experimental facility that was specifically design and constructed for this purpose. The heat transfer rate and the coefficient of heat transfer increases with perforation diameter increased.

DETERMINATION OF THE TEMPERATURE DISTRIBUTION THE PERFORATED FINS UNDER

This work treats the problem of heat transfer for perforated fins under natural convection. The temperature distribution is examined for an array of rectangular fins (15 fins) with uniform cross-sectional area (100x270 mm) embedded with various vertical body perforations that extend through the fin thickness. The patterns of perforations include 18 circular perforations (holes). Experiments were carried out in an experimental facility that was specifically design and constructed for this purpose. The heat transfer rate and the coefficient of heat transfer increases with perforation diameter increased.

Equivalent thickness of cold-formed thin-walled channel sections with perforated webs under compression

Cold-formed thin-walled channel sections with perforated webs (thermal studs) are widely used in external wall panels in cold regions to reduce the cold bridging effect. However, no design method appears to be available for this type of structure. A possible method is to convert the perforated web of a thermal stud into a solid one with a reduced thickness (which is referred to as the equivalent thickness) and then adopt an existing design method for solid sections (e.g. EN 1993-1-3). This paper presents the development of a method to calculate the equivalent web thickness. The equivalent thickness calculation equation is based on regression analysis of a large number of finite element simulation results of elastic local buckling strength of perforated plates under compression, considering the effects of a number of different design variables such as plate depth, thickness, perforation patterns and dimensions of the plate. The FE simulations were carried out using a general FE software. This study suggests that the equivalent thickness is mainly related to the plate width to thickness ratio, the total width of perforation at the critical section and the width of the perforation zone (total plate width between the first and last perforation). A regression equation has been proposed to relate the equivalent thickness to these parameters. To demonstrate the validity of the proposed equivalent thickness method, the compression strengths of a large range of perforated columns have been simulated by using either the original perforated sections or the equivalent solid section; and a comparison of the simulation results shows good agreement between the two sets of results.

Typhoid intestinal perforation under 5 years of age

Typhoid intestinal perforation is an important cause of morbidity and mortality in many developing countries. The peculiar features in children <5 years old need to be recognised in order to improve outcome. To determine the characteristic pattern and outcome of typhoid intestinal perforation in children under 5 years of age in south-east Nigeria. Comparative analysis of 83 children with typhoid intestinal perforation between January 2001 and December 2006 at the University of Nigeria Teaching Hospital, Enugu. There were 22 (26.5%) children <5 years of age and 61 (73.5%) >5 years. In the younger children, the predominant presentation was fever, vomiting and abdominal tenderness, and in the older children it was fever, abdominal pain and distension. Features of peritonitis were present in only 54.5% aged <5 years compared with 90.2% of the older children (p<0.001). The average number of perforations in the under-5s was 2.1 (range 1-4) and >1.3 (range 1-3) in the older children (p<0.01). The types of operative procedure (simple closure and segmental bowel resection) were similar in both groups. Post-operative complications were not significantly different in the two groups and included surgical wound infection, prolonged ileus, pulmonary infection, wound dehiscence, re-perforation, intra-abdominal abscess and incisional hernia. There were nine (40.9%) deaths in the <5s and 12 (19.7%) in the >5s (p<0.05). Typhoid intestinal perforation in children <5 is associated with atypical presentation and high mortality. A high index of suspicion will ensure earlier presentation and might improve outcome.

Fatal Gastrointestinal Perforations in sudden death cases in Last 10 years at UMMC- Malaysia

Gastrointestinal perforation occurs when the wall of the gastro-intestinal tract like stomach, small intestine or large bowel develops a hole through its entire thickness. This retrospective study was aimed to identify pattern of GIT perforations that caused sudden deaths in this part of the world. The study was conducted in Forensic Pathology unit of University Malaya, Kuala Lumpur in the year 2006 by reviewing the autopsy reports. There were 61 cases of GIT perforation out of 5579 autopsies conducted during a period of ten years (1996-2005). The incidence rate of fatal gastrointestinal perforation was 1.09% during this period. Out of these 61 cases, there were 49 males (80.3%) and 12 female (19.7%). The most common site of gastrointestinal perforation was at the stomach (45.7%), followed by duodenum (18.5%), esophagus (9.9%), small intestine (9.9%), and large intestine (16.0%). The 36.07% cases had positive correlation with at least one of the known risk factors. Keywords : Gastrointestinal perforation, peptic ulcer perforation, peritonitis, sudden deaths, silent perforations in sudden death, autopsy. Internet Journal of Medical Update Vol. 2 (1) 2007: pp. 29-32

Effect of non-uniform perforation in the long concentric resonator on transmission loss and back pressure

It is known that the acoustical and, possibly, mechanical performance of the perforated resonator can be controlled by the porosity and distribution of holes. To analyze the effect of the porosity distribution pattern on resonator performance, in particular under the design condition of restricted volume, five typical perforation patterns of an acoustically long concentric resonator were investigated experimentally and numerically. Transmission loss and back pressure were used to represent the acoustic and mechanical performance indices, respectively. Prediction of transmission loss was made by segmental decoupling analysis with an empirical impedance model of orifices. Prediction of back pressure was done by computational fluid dynamics analysis. The overall trend of the calculated results matched well with the measured results. In terms of acoustic performance, it is noted that a specific frequency range was mostly influenced by the change of axial porosity pattern. For mechanical performance, a gradual change in porosity played a dominant role in stabilizing the flow field and static pressure distribution. It is concluded that an axial perforation pattern with a gradual change in porosity yields the best performance by forming a flow field with minimized loss and an acoustic field dominated by a quarter-wavelength resonance of equivalent extended pipes. In particular, the most preferred perforation pattern in terms of transmission loss and back pressure was the one with gradually increasing porosity from the upstream part and gradually decreasing porosity from the middle part as far as the downstream end.

Improvement of air distribution in refrigerated vertical open front remote supermarket display cases

This paper presents some of the results derived from extensive experimentation on display cases for supermarkets and derives some possible improvements to augment temperature uniformity and energy performance. The effect of the perforation pattern of the rear duct on the distribution of airflow between these and the front curtain is brought out. The critical component is air infiltration across the curtain, which is governed by internal air distribution and curtain characteristics. It is observed that a 70–30 distribution of flow between the curtain and the rear duct perforations yields a performance that satisfies the standards. Further, a judicious distribution of perforations on the rear duct at various levels and across is necessary. Correlations available in the literature are useful in making a qualitative assessment of the results.

Accuracy Analysis of Pedicle Screw Placement in Posterior Scoliosis Surgery

The accuracy of pedicle screw placement was evaluated in posterior scoliosis surgeries with or without the use of computer-assisted surgical techniques. In this retrospective cohort study, the pedicle screw placement accuracy in posterior scoliosis surgery was compared between conventional fluoroscopic and computer-assisted surgical techniques. There has been no study systemically analyzing the perforation pattern and comparative accuracy of pedicle screw placement in posterior scoliosis surgery. The 45 patients who received posterior correction surgeries were divided into 2 groups: Group C, manual control (25 patients); and Group N, navigation surgery (20 patients). The average Cobb angles were 73.7 degrees and 73.1 degrees before surgery in Group C and Group N, respectively. Using CT images, vertebral rotation, pedicle axes as measured to anteroposterior sacral axis and vertebral axis, and insertion angle error were measured. In perforation cases, the angular tendency, insertion point, and length abnormality were evaluated. The perforation was observed in 11% of Group C and 1.8% in Group N. In Group C, medial perforations of left screws were demonstrated in 8 of 9 perforated screws and 55% were distributed either in L1 or T12. The perforation consistently occurred in pedicles in which those axes approached anteroposterior sacral axis within 5 degrees . The average insertion errors were 8.4 degrees and 5.0 degrees in Group C and Group N, respectively, which were significantly different (P < 0.02). The medial perforation in Group C occurred around L1, especially when pedicle axis approached anteroposterior sacral axis. This consistent tendency was considered as the limitation of fluoroscopic screw insertion in which horizontal vertebral image was not visible. The use of surgical navigation system successfully reduced the perforation rate and insertion angle errors, demonstrating the clear advantage in safe and accurate pedicle screw placement of scoliosis surgery.

Fracture strength in randomly perforated plates

We have measured the forces that need to be applied quasistatically to randomly perforated rectangular aluminum plates to tear them apart. Concomitantly, for identical geometrical structures, we have carried out numerical simulations of the tearing process. The two results agree quite reasonably, and especially so for perforated area densities (P) that are rather less than the critical percolation densities. A given value of P can be achieved through various different realizations (patterns of perforations), each with a somewhat different fracture (or failure) strength F. Our results predict empirically an “expected F” [F¯(P)] and an expected standard deviation [root variance, S(P)] as functions of P. This enables the risk analysis of failures in plates under tensile stress, which is needed in, e.g., the estimation of the flying safety of a spacecraft subject to multiple perforations.

A DETAILED DESCRIPTION OF A DANISH STRAIN OF NITZSCHIA SIGMOIDEA, THE TYPE SPECIES OF NITZSCHIA, PROVIDING A REFERENCE FOR FUTURE MORPHOLOGICAL AND PHYLOGENETIC STUDIES OF THE GENUS

Nitzschia sigmoidea is the type species of the diatom genus Nitzschia. Recent evidence implies that the genus is polyphyletic. As a reference for future studies of the genus, we here provide a thorough morphological examination of the silica frustule, including new details of copulae and poroids, as well as compiling previously published information on the cellular ultrastructure. Observed specimens of Nitzschia sigmoidea are linear in frustule view and sigmoid in girdle view with a length of 346–359 μm, and a width of 9–13 μm. Both nitzschioid and hantzschioid cells are found. The raphe is highly eccentric, elevated on a keel, without a central nodule. The raphe ends externally in a hook-shaped terminal fissure, internally in a helictoglossa forming an excrescence. Tubular fibulae are slim and irregularly distributed with a density of 6–9 in 10 μm. A conopeum runs the entire length of the cell. The striae are uniseriate with 4–5 poroids in 1 μm, each with a hymen with a hexagonal pattern of perforations. Two types of copulae are found, both with two rows of poroids, 3.2–3.4 poroids in 1 μm. One type of copula is fimbriate with evenly distributed fimbriae, while the other type has a veil. Initially, growth of the diatom was restricted by lack of carbon in the freshwater medium, after addition of bicarbonate it grew well. HPLC analysis showed no domoic acid production by N. sigmoidea.

Bedload abrasion and the in situ fragmentation of bivalve shells

AbstractThe aim of this study was to determine how Unio bivalve shells fragment within the channel of the Sakmara River (southern Urals, Russia). The Sakmara River has an abundant bivalve population and a highly variable flow regime which, at low flow, allowed much of the channel bed to be examined. A large data set of 1013 shells (Unio sp.) was examined and these were shown to have consistent patterns of orientation, aspect, shell abrasion, perforation and fracture. The close spatial relationship between areas of shell abrasion, shell perforation and shell fracture showed that they form part of a continuum whereby areas of abrasion evolve into perforations and perforations coalesce and enlarge into fractures. The mechanism of shell damage proposed is one of abrasion in place, whereby the shell remains stationary on the surface of the point bar and is impacted by bedload. Underpinning this process are the hydrodynamic properties of the bivalve shell, with consistency in the orientation and aspect of the valve in a flowing current producing consistency in the distribution of damage on the shell surface. Valves preferentially lie in a convex‐up position and orientate in the flow such that the umbo faces upstream. The elevated, upstream‐facing umbo region is exposed to particle impact and is the first to be abraded and perforated. The vulnerability of the umbo to perforation is greatly increased by the thinness of the shell at the umbo cavity. The in situ abrasion process is enhanced by the development of an armoured gravel bed which restricts valve mobility and maintains shells within the abrasion zone at the sediment–water interface. The in situ abrasion process shows that broken shells are not a reliable indicator of long distance transport. The study also raises the issue that tumbling barrel experiments, which are generally used to simulate shell abrasion, will not replicate the type of directionally focused sand‐blasting which appears to be the principal cause of shell fragmentation in the Sakmara River.

Patterns of Venous Reflux and Obstruction in Patients With Skin Damage Due to Chronic Venous Disease

Identified were characteristics of individuals with skin damage related to chronic venous disease. Patients with chronic venous disease (n = 164) were evaluated with duplex ultrasound imaging and were placed in classes 4, 5, and 6 according to the CEAP classification. Their findings were compared with 100 class 2 controls. The prevalence of deep venous thrombosis was higher in the study group (23.7%) versus controls (5.1%; P < .0001), as was the prevalence of deep, perforator, and combined patterns of disease (P < .0001, P < .0007, and P < .0001). The mean duration of disease in controls 2 was shorter compared with the study group (P = .0019). The prevalence of reflux and obstruction within the study group was higher than in controls (P = .0021). Skin changes accurately reflect severity of chronic venous disease. Superficial and perforator vein reflux is the major cause of disease.

Behind-armor debris from the impact of hypervelocity tungsten penetrators

Behind-armor debris is the main mechanism by which targets are destroyed by projectile impact. The behind-armor debris generated from the impact of tungsten heavy alloy (THA) penetrators with a length-to-diameter ratio ( L/ D) of 20 against 6061-T6 aluminum targets was characterized. Behind-armor debris characteristics described were the number of debris particles, their positions, and their size distribution. Experiments were performed against two nominal target thicknesses, 100 and 150 mm, and covered a velocity range from 1.7 to 2.6 km/s. Two methods of obtaining data were used—radiographs were taken of the behind-armor debris, and perforation patterns were generated on steel witness packs placed behind the aluminum target. Debris particles recovered from the witness packs were also studied. Results are discussed for the effect of changes in target thickness and impact velocity on behind-armor debris particle characteristics.

Typhoid intestinal perforation in children: a continuing scourge in a developing country

Typhoid intestinal perforation is a principal cause of morbidity and mortality affecting both adults and children. This study aims to evaluate the pattern of typhoid intestinal perforation and outcome of its management in Nigerian children. The records of consecutive children managed for typhoid intestinal perforation at Juth, between 1996 and 2005 have been reviewed. There were 184 children (M:F = 1.04:1), with a mean of 5.8 years (range 4 to 15 years). More than a half (62.5%) of the patients were in the 5-6 year age group. The incidence peaked in April-May, and November-December. Increased incidence of typhoid perforation was observed between 2002 and 2005. All patients presented with the classic features of typhoid enteric perforation. Hypokalaemia and anaemia were common at presentation. Only 75 (40.6%) patients had operation within 24 h of perforation. The types of surgery included simple excision of the edges of the peroration and closure (74.5%), wedge resection and closure in (14.5%), segmental resection with primary end-to-end anastomosis (3.6%) and right hemi-colectomy with ileo-colic or ileo-transverse anastomosis. Wound infection and dehiscence, anastomotic breakdown with faecal fistula, intra peritoneal abscesses and chest infections were the main post operative complications. The overall mortality rate was 22.8 (42). Excision and simple closure was associated with the least incidence of anastomotic breakdown and operation time. The incidence of typhoid intestinal perforation is on the increase at our institution. Early limited surgery provides optimal results.

Design and performance of materials for subsurface drainage systems in agriculture

During the second half of the 20th century, numerous land drainage systems using new materials for the drain channels that often function inadequately due to biochemical and mechanical clogging, were developed. The design of drainpipes and envelope materials used for these land drainage systems was based on both theoretical and experimental investigations. This contribution reviews the simultaneous development of theory and practical experience in Europe and North America. The results of the effect of perforation shape and pattern in drainpipes and of envelope materials on drainage performance are summarized and the latest design criteria of granular materials and synthetic envelopes presented. Theoretical investigations are associated with field data on the performance of drainage materials. A thorough knowledge, not only of the flow conditions, but also of the physical soil properties in the vicinity of the drains is imperative for a correct interpretation of field data. This contribution represents the main features on drainpipes and envelope materials, and the physical soil processes that occur in the vicinity of the drain. It gives an overview of the research work done referring to numerous publications where relevant and detailed information can be found.

Characterization of microwave photonic band-gap structures with bandpass filter applications

Microwave photonic band-gap (PBG) structures are well known for their superior ability to generate a band stop effect at a certain frequency range. Together with the microstrip transmission line structure, PBG can be utilized as a filter exceptionally well since the periodic perforation patterns can be implemented easily in the ground plane. In this research work, square perforations of different dimensions are constructed in the ground plane of a microstrip transmission line to achieve a double band stop PBG structure. Thus, the transmission ability of the microstrip line is being blocked at different frequency ranges to create a bandpass filter. It is found that the bandpass frequency is strongly dependent on the dimension to period distance ratio. It is demonstrated in both simulation and measurement that the bandpass region can be created at high frequency above 10GHz.