Hexagonal Openings Research Articles

Web buckling study of the behaviour and strength of perforated steel beams with different novel web opening shapes

This paper presents an experimental and analytical study on the behaviour of perforated steel beams with closely spaced web openings. Seven specimens including two typical cellular beams (i.e. circular web openings) and five perforated beams with novel web opening shapes were tested to investigate the failure mode and load strength of the web-post between two adjacent web openings. Fourteen numerical test specimens were developed and analysed by the finite element method and the results were compared with the full scale experiments. The effect of web opening spacing/web opening depth of web-posts was studied to investigate the effective ‘strut’ action of the web-post buckling. The effect of the web opening depth/web thickness was also studied to investigate the stability (slenderness) of the web-post subjected to vertical shear load. Two hundred and twenty-fine elastic-plastic finite element analyses were then employed in a comprehensive parametric study to propose an empirical formula which predicts the ultimate vertical shear load strength of web-posts formed from the particular web opening shapes. Perforated beams with standard circular, hexagonal and elongated web openings are mostly used nowadays. Various non-standard web opening shapes are introduced through this paper for first time. These new pioneering web opening shapes improve the structural performance of the perforated beams when examined under the web-post buckling failure mode. In addition, the manufacturing procedure of these non-standard web openings show great advantage in comparison with the manufacturing way of the more popular cellular beams.

SU-FF-T-152: Development of a Variable-Aperture Collimator for Small Animal Radiation Therapy

Purpose: An automatic variable-aperture collimator has been developed to use a diagnostic animal CT for small animal radiation therapy. This system, together with a 3D translation bed stage, will enable the application of advanced clinical radiotherapy techniques to animal models of disease. Method and Materials: The collimator is mounted on the gantry of a GE RS120 microCT scanner (GE Medical Systems, Milwaukee, WI), between the x-ray source and the bore. It consists of two stages offset by 30°, each with 6 trapezoidal brass blocks moving along a hexagonal frame, pushed by 3 slots on a rotational driving plate to create hexagonal openings. The openings of the two stages always form a constant ratio, to fit with the microCT x-ray beam divergence. The collimator axis to x-ray beam alignment has been assessed by imaging the aperture. An algorithm has been developed to measure the misalignment and to guide the collimator position adjustment. The torques required to drive the two stages were measured by a torquemeter during the design. Results: Geometric analyses and direct measurement demonstrated that the projected aperture on the isocenter plane is 3.5 mm/degree of driving plate rotation. The collimator can provide 98% of attenuation for 120 keV photons, sufficient for therapeutic narrow beam generations. The collimator-beam alignment can be adjusted to better than 0.2 mm, compared with the 0.3-mm source spot size. With the designed ratio of the openings, a regular dodecagonal aperture is formed from the source view. The measured torque to open and close a stage ranges from 1 to 5 N-m. A 30-N-m driving motor has been selected accordingly. Conclusion: A variable-aperture collimator has been constructed. Using a commercial animal CT one can deliver narrow beam x-ray to experimental animals, so that advanced clinical radiation therapy techniques can be applied in pre-clinical research.

Anomalous Anisotropic Etching of (111) and (100) Silicon Wafers Using Acidic Solutions

We report anisotropic chemical wet etching of (111) and (100) silicon wafers using an acidic solution. The etching is performed using a solution consisting of hexafluorosilicic acid and nitric acid. For silicon samples with orientation, the etching results in the formation of crystallographic features with hexagonal openings. The walls of the crater are assumed to be different planes with their crossing with planes. Extended periods of etching result in the formation of scale-repeated features resembling the fractal structures. Etching of a silicon was also been examined, which indicated the evolution of concave corners and and planes.

Effects of Cope Geometry on the Strength and Behavior of Cellular and Castellated Beams

This paper reviews an experimental and analytical investigation of the effect of cope geometry ( distance) on the strength and failure behavior of non-composite, doubly symmetric, uniformly loaded open web expanded beams. Thirty-six (36) beams, eighteen (18) cellular (circular openings) and eighteen (18) castellated (hexagonal openings), of various cope geometries and depths, each instrumented to measure load, strain and displacement, were tested to failure. A linear elastic finite element (FE) analysis for service loading conditions and a nonlinear FE buckling analysis were performed in parallel with the experimental testing program. The experimentally validated models were then extended to uncoped and intermediately coped beam geometries to investigate the effect of cope geometry on beam capacity and failure mode. Through this study, it was found that failure loads for the beams exceeded calculated design loads (ASD) by a minimum factor of 1.8 regardless of cope size or beam type. Further, cellular beams experienced less percent capacity loss with increasing cope size than did castellated beams.

Characterization of AlInGaN quaternary epilayers grown by metal organic chemical vapor deposition

Two sets of AlInGaN quaternary epilayers grown by metal organic chemical vapor deposition (MOCVD) were studied by atomic force microscopy (AFM), high-resolution X-ray diffraction (HR-XRD) and photoluminescence (PL) spectroscopy. In all samples a large number of pits have been observed on the surface with the density of 1×10 9 cm −2, and hexagonal opening. In one set with different thickness, it was also found that the XRD angle separation between GaN and AlInGaN diffraction peaks increased with the thickness. In PL measurements, a blue shift of the PL peak from AlInGaN was found as the thickness increased. The origin of these observations was proposed to be the Al composition pulling effect. In the other set with different Al/In ratios, domain features were observed on the surface of AlInGaN epilayers with high Al/In ratio. The surface roughness increased as Al/In ratio decreased. PL emission from AlInGaN became stronger as the Al/In ratio approached the lattice-match condition. When the Al/In ratio was below that of lattice-match condition, the emission peak was enhanced and broadened dramatically at the same time, indicating the effect of indium clustering in AlInGaN epilayers.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (1 1 1)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO 2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {1 1 0} vertical facets with their diameter of order of 100 nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60 nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Growth of GaAs/AlGaAs hexagonal pillars on GaAs (111)B surfaces by selective-area MOVPE

We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO2-masked (1 1 1)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 100nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60nm and large aspect ratio (>100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth.

Growth and Optical Properties of 2D Photonic Crystals Based on Hexagonal GaAs/AlGaAs Pillar Arrays by Selective-Area Metalorganic Vapor Phase Epitaxy

ABSTRACTWe report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar arrays using selective area (SA) metalorganic vapor phase epitaxy (MOVPE) for the application of two-dimensional photonic crystals (2D-PhCs). SA-MOVPE was carried out on SiO2 masked (111)B GaAs substrates with circular or hexagonal hole openings. Extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 200 nm were obtained. Unexpectingly strong intense light emission was observed for the room temperature photoluminescence measurement, which suggests low surface nonradiative recombination and enhancement of the light extraction efficiency of the pillar arrays.

Formation of Al xGa 1− xAs periodic array of micro-hexagonal pillars and air holes by selective area MOVPE

A two-dimensional (2D) periodic array having air/semiconductor interfaces can be applied to photonic crystals (PCs), which are expected to control spontaneous emission and optical transports in the next-generation devices. In this paper, we report on the selective area metal-organic vapor phase epitaxial (SA-MOVPE) growth of a Al x Ga 1− x As 2D periodic array on a GaAs (1 1 1)B substrate for application to 2DPCs having GaAs/AlGaAs heterostructures. Al x Ga 1− x As ( x=0, 0.25 and 0.50) growth was carried out on triangular lattice array of hexagonal GaAs openings and hexagonal SiN x masks. A uniform Al 0.50Ga 0.50As hexagonal pillar array and a GaAs hexagonal air-hole array with a 1 μm-period were successfully obtained. The important growth parameter for uniform 2DPC structure formation by SA-MOVPE was clarified. Furthermore, we describe the successful demonstration of a 400 nm-period pillar array and an air-hole array, which corresponds to the optical communication wavelength λ=1.3–1.55 μm. The results indicate that SA-MOVPE method is very promising for the formation of uniform semiconductor 2DPCs without the occurrence of process-induced damages.

Spatially resolved photoluminescence of laterally overgrown GaN

The epitaxial lateral overgrowth (ELOG) of GaN has recently proven to be a suitable technique to significantly reduce the dislocation density in metalorganic vapor phase epitaxy (MOVPE) or hydride vapor phase epitaxy (HVPE) of GaN. We have investigated by spatially resolved photoluminescence on GaN overgrown from hexagonal openings and partially coalesced pyramids obtained by MOVPE. Different positions of the overgrowth were analyzed, i.e., the edge of the coalesced pyramid, the center, the starting pyramids and GaN underneath the dielectric. Whereas the photoluminescence (PL) spectra of starting pyramids and GaN underneath the dielectric behave about the same, a drastic difference between edge and center of coalesced pyramids is observed. Two PL bands are observed at 300 K, the band edge one, at 3.41 eV, and the yellow luminescence (YL) around 2.2 eV. The highest intensity of the 3.41 eV peak comes from the edge of the overgrowth, the lowest from the center. Conversely, the YL intensity is the strongest at the center of the overgrowth, once again by one order of magnitude. In addition, the YL could be resolved into overlapping gaussian lines, each of them corresponding to a given LO phonon replica. The lineshape is analyzed in the frame of configuration coordinate diagram, and the zero phonon line estimated to be at 2.53 eV.

Magnesium induced changes in the selective growth of GaN by metalorganic vapor phase epitaxy

Atmospheric pressure metalorganic vapor phase epitaxy is used to perform selective regrowth of GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. The basic pattern is constituted by a 15 μm period hexagonal array of hexagonal openings in the mask, these openings being circumscribed into 10 μm diam circles. We investigate the effect of Mg incorporation on the growth anisotropy of the localized GaN islands by varying the ratio [Mg]/[Ga] of bis-methylcyclopentadienyl-magnesium and trimethylgallium partial pressures. Both undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R (1 1̄01) facets, are achieved with a good selectivity. It is found that the GaN growth rates VR and VC, measured in the R〈11̄01〉 and C 〈0001〉 directions respectively, are drastically affected by the Mg incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/VC ratio can be increased so that the delimiting top C facet does not vanish as usually observed in undoped GaN localized growth, but by contrast expands.

Effect of Magnesium and Silicon on the lateral overgrowth of GaN patterned substrates by Metal Organic Vapor Phase Epitaxy

Metalorganic vapor phase epitaxy was used to achieve selective regrowth of undoped, Mg- and Si-doped GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. Hexagonal openings in the mask defined into 10 µm diameter circles separated by 5µm were used as a pattern for the present study. Uniform undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R {101} facets, were achieved with a good selectivity. Si-doped GaN hexagonal pyramids delimited by vertical {100} facets and (0001) top facet were obtained for a high SiH4 flow rate in the vapor phase. We found that the GaN growth rates VR and VC, measured in the R <101> and C <0001> directions respectively, were drastically affected by the Mg and Si incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/VC ratio can be increased. Hence, the delimiting top C facet do not vanish as usually observed in undoped GaN selective regrowth but conversely expands. On the other hand, under proper growth conditions, 20µm-high Si-doped GaN columns were obtained.

Three new species of oxyuroid nematodes, including two new genera, from freshwater catfishes in Brazil

Three new oxyuroid nematode species of the family Pharyngodonidae are described from the intestine of freshwater catfishes in Brazil (River Parana), two of them being representatives of new monotypic genera: Ichthyouris brasiliensis n. sp. from Pterygoplichthys aculeatus, Brasilnema pimelodellae n. g., n. sp. from Pimelodella gracilis, and Parasynodontisia petterae n. g., n. sp. from Rhinelepis aspera. I. brasiliensis n. sp. differs from the only other congeneric species, I. ro, mainly in the absence of a pair of plate-like structures in the male caudal region, shorter caudal alae, the presence of a pair of conspicuous lateral spines at the level of the anal opening in the female and by other features. Brasilnema n. g. is characterised mainly by a hexagonal oral opening, a broad buccal capsule containing three teeth, a simple spicule and an amphidelphic uterus, whereas Parasynodontisia n. g. is characterised by a triangular oral opening and an amphidelphic uterus in the female; both genera possess six small, triangular, circumoral lamellae slightly raised above the apical surface. The paper includes a key to the pharyngodonid genera whose species are parasitic in fishes.

Primary and diagenetic microstructures in trilobites

McAllister, John E. & Brand, Uwe 1989 01 15: Primary and diagenetic microstructures in trilobites. Lethaia, Vol. 22, pp. 101–111. Oslo. ISSN 0024–1164. Ordovician and Devonian trilobites were studied by scanning electron microscopy (SEM) to define primary and diagenetic microstructures. Primary structures such as Osmólska cavities and hexagonal surface openings are present in samples obtained from both shale and limestone lenses in shales. Generally, samples with primary microstructures are also geochemically well preserved. Diagenetic microstructures were found in samples from shales and limestones, but those from limestones are the most geochemically and microstructurally altered. ‘Dendritic’ patterns and fused matrices were found in the altered cuticles of trilobites of different species and ages and are therefore considered a normal feature of the diagenetic alteration of cuticular calcite. Primary and diagenetic microstructures of trilobite cuticles are independent of size, species and age of the specimens, but are largely controlled by lithology and thus diagenesis. *Trilobita, primary-, diagenetic microstructures, fossil diagenesis.

On the parameters affecting the track opening geometry in biotite mica

The bulk etch rate parallel to the cleavage planes of biotite mica increases exponentially with the concentration of the etchant (HF). The track opening shape in biotite can be changed by altering the crystallographic structure of mica by means of external irradiations prior to the irradiation of the sample with fission fragments or heavy ions. For alpha particles and electron doses of greater than 3 × 10 8 Gy the openings of the normally incident fission tracks become circular, as compared with the hexagonal track openings in unirradiated samples. It is shown that the track opening geometry also depends on the amount of radiation damage present in the track core.

Deet-impregnated net shirt repels biting flies.

Mosquitoes, tabanids, punkies, black flies, and other blood-sucking Diptera are often the bane of field researchers, sportsmen, and laborers in many areas. A few years ago I read an abstract of a Soviet paper concerning the use of net shirts impregnated with diethylamidemetatoluate for invididual protection against biting flies (Cherapanov and Gomoyunova 1963). Using the abstract as a guide I made several net shirts from “mosquito bar” material and soaked them each in 200 ml of 30% technical deet (Metadelphene®, Hercules Powder Co., Wilmington, Del.) in alcohol. The shirts were of loose hooded ski-jacket design with elastic at bottom, wrist, and hood openings. The net material was woven cotton-rayon mosquito bar cloth with hexagonal openings (13/in.).