Concave Deformation Research Articles

Simulation analysis for ion assisted fast ignition using structured targets

As the heating efficiency by fast electrons in the fast ignition scheme is estimated to be very low due to their large divergence angle and high energy. To mitigate this problem, low-density plastic foam, which can generate not only proton (H+) but also carbon (C6+) beams, can be introduced to currently used cone-guided targets and additional core heating by ions is expected. According to 2D PIC simulations, it is found that the ion beams also diverge by the static electric field and concave surface deformation. Thus structured targets are suggested to optimize ion beam characteristics, and their improvement and core heating enhancement by ion beams are confirmed.

Visualization study on bubble dynamical behavior in subcooled flow boiling under various subcooling degree and flowrates

An experimental study was conducted to investigate the characteristics of bubble dynamical behavior in subcooled flow nucleate boiling in an upward annular channel. The bubble dynamical behavior under wide ranges of subcooling degrees (ΔTsub=5–50K) and flowrates (vm=0.1–0.8m/s) were observed and recorded with high spatial and temporal resolutions by using a high speed video camera and a Cassergrain microscopic lens. The bubble behaviors at different subcooling degrees and flowrates were found to be quite different. At a medium subcooling degree, the bubble deformation at upstream-side interface during its growing and departure period was observed and was attributed to the condensation caused by the cold liquid coming from the subcooled bulk flow. At high subcooling degrees and low flowrates, contracting deformation was found in both upstream and downstream bottom of the bubble, the phenomenon of two successive bubbles was also observed. At high subcooling degrees but high flowrates, bubble was strongly pushed by the incoming liquid flow and concave deformation in the middle of bubble upstream-side interface was observed. At lower subcooling degrees, bubble behaviors at different flowrates are quite similar. The bubble shape was very close to a sphere, only very weak deforming phenomena was observed.

Experimental and numerical research on out-of-plane flexural property of plates reinforced SHS X-joints

The static tests of 13 SHS X-joints with different brace to chord side length ratios and different types of plates reinforcement under out-of-plane bending in brace were carried out. Experimental test schemes, failure modes of specimens, moment–vertical displacement curves, moment–deformation of the chord, and strain strength distribution curves were presented. The effects of brace to chord side length ratios and plates reinforcement types on out-of-plane flexural property of SHS X-joints were studied. Results show that punching shear of chord face disappeared, concave and convex deformation of chord decreased when either collar plates or doubler plates were welded on chord face. Moment–vertical displacement curves of all specimens have obvious elastic, elastic–plastic and plastic stages. As brace to chord side length ratio increased, the out-of-plane flexural ultimate capacity and initial stiffness of joints with the same plates reinforcement type increased, but ductility of joints decreased. With the same brace to chord side length ratio, the out-of-plane flexural initial stiffness and ultimate capacity of collar plates reinforced joints, doubler plates reinforced joints and unreinforced joints decreased progressively. Thickness of reinforcement plates had an obvious effect on out-of-plane ultimate capacity of SHS X-joints. Thickness of reinforcement plates had no obvious effect on out-of-plane flexural initial stiffness of SHS X-joints when the value of reinforcement plates to chord wall thickness ratio exceeds 1.0. As thickness of reinforcement plates increased, the ductility of reinforced X-joints decreased. The concave and convex deformation of every specimen had good symmetry. The design equations were proposed for collar and doubler plates reinforced SHS X-joints under out-of-plane bending, which were shown to be accurate and reliable.

In situ observation of meniscus shape deformation with colloidal stripe pattern formation in convective self-assembly.

Vertical convective self-assembly is capable of fabricating stripe-patterned structures of colloidal particles with well-ordered periodicity. To unveil the mechanism of the stripe pattern formation, in the present study, we focus on the meniscus shape and conduct in situ observations of shape deformation associated with particulate line evolution. The results reveal that the meniscus is elongated downward in a concave fashion toward the substrate in accordance with solvent evaporation, while the concave deformation is accelerated by solvent flow, resulting in the rupture of the liquid film at the thinnest point of the meniscus. The meniscus rupture triggers the meniscus to slide off from the particulate line, followed by the propagation of the sliding motion of the three-phase contact line, resulting in the formation of stripe spacing.

Plate reinforced square hollow section X-joints subjected to in-plane moment

The static test of 13 square hollow section (SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry; as β increases, the yield and ultimate deformation of chord decrease.

Investigations on crack generation mechanism and crack reduction by buffer layer insertion in thermal-plasma-jet crystallization of amorphous silicon films on glass substrate

The crack generation mechanism and the effect of crack reduction by buffer SiO2 layer insertion in thermal-plasma-jet (TPJ) crystallization of an amorphous silicon film on a glass substrate have been investigated. The crack generation was clearly observed 13.7 s after TPJ irradiation using a high-speed camera, which indicates that cracks are generated not during heating, but during cooling. From the measurement and simulation of substrate deformations, it was clarified that the substrate deformed convexly during heating and it consequently deformed concavely after cooling owing to the substrate surface densification. This result indicated that the tensile stress generated by the concave deformation is the origin of cracks. The deposition of the buffer SiO2 layer generated compressive stress, which minimizes accumulation of tensile stress after TPJ annealing. The number of cracks in unit length significantly decreased owing to the decrease in tensile stress with the increase in the thickness of the buffer SiO2 layer.

Process for design optimization of honeycomb core sandwich panels for blast load mitigation

A general process for optimization of a sandwich panel to minimize the effects of air blast loading is presented here. The panel geometry consists of two metal face plates with a crushable honeycomb or other type of core. Optimization is necessary as there is strong coupling between the several variables and the physics, which makes parametric studies relatively ineffective. Virtual testing is used to develop a homogenized model for the stress---strain curve of the honeycomb core, which can be readily applied to other types of cellular core. The homogenized model has been validated by comparison to existing results as well as to results from detailed finite element (FE) models. A design of experiments (DOE) based response surface optimization method in combination with LS-DYNA is used to minimize dynamic deflection or acceleration of the back face plate. Constraints on total mass and on plastic strain in the face plates are imposed. The mechanism of lowering the backface deflection is by increasing front face plate thickness which effectively distributes the blast load to a larger area of the core and avoids local concave deformation of the front face plate. Further, core depth is increased which increases panel stiffness. For acceleration minimization, results again produce a stiffer front face plate, but accompanied by a sufficiently soft core. The mechanism of lowering the backface acceleration is by absorbing energy with low transmitted stress. A clear cut comparison between monolithic metal plates and sandwich plates, for the same loading and failure criteria, is presented here.

Changes of Corneal Biomechanics With Keratoconus

To perform advanced analysis of the corneal deformation response to air pressure in keratoconics compared with age- and sex-matched controls. The ocular response analyzer was used to measure the air pressure-corneal deformation relationship of 37 patients with keratoconus and 37 age (mean 36 ± 10 years)- and sex-matched controls with healthy corneas. Four repeat air pressure-corneal deformation profiles were averaged, and 42 separate parameters relating to each element of the profiles were extracted. Corneal topography and pachymetry were performed with the Orbscan II. The severity of the keratoconus was graded based on a single metric derived from anterior corneal curvatures, difference in astigmatism in each meridian, anterior best-fit sphere, and posterior best-fit sphere. Most of the biomechanical characteristics of keratoconic eyes were significantly different from normal eyes (P < 0.001), especially during the initial corneal applanation. With increasing keratoconus severity, the cornea was thinner (r = -0.407, P < 0.001), the speed of corneal concave deformation past applanation was quicker (dive; r2 = -0.314, P = 0.01), and the tear film index was lower (r = -0.319, P = 0.01). The variance in keratoconus severity could be accounted for by the corneal curvature and central corneal thickness (r = 0.80) with biomechanical characteristics contributing an additional 4% (total r = 0.84). The area under the receiver operating characteristic curve was 0.919 ± 0.025 for keratometry alone, 0.965 ± 0.014 with the addition of pachymetry, and 0.972 ± 0.012 combined with ocular response analyzer biomechanical parameters. Characteristics of the air pressure-corneal deformation profile are more affected by keratoconus than the traditionally extracted corneal hysteresis and corneal resistance factors. These biomechanical metrics slightly improved the detection and severity prediction of keratoconus above traditional keratometric and pachymetric assessment of corneal shape.

Design and manufacturing of the antechamber for BEPCII storage rings

Antechamber which composes the arc vacuum chamber of storage rings is one of the key devices of BEPCII. It has the characteristic of various specifications, large size, complex structure, and high dimension accuracy. This paper gives a review on the structure features and the procedure of production, including the mechanical machining process, cleaning and welding process of high vacuum aluminum alloy, ultrahigh vacuum test and so on. In view of the occurrence of the concave deformation, the reasons are analyzed and the correction method developed is introduced too.

Simulation and Characterization of a Novel Large Stroke Micromirror

This paper reports on the simulation and characterization of a microelectromechanical system (MEMS) micromirror fabricated with PolyMUMPs. The overall diameter of the hexagonal micrimirror, including mirror plate and 3 supporting cantilevers fixed around, is 450um. A 3D model is built in finite element method (FEM) with COMSOL. Simulations of the elevated height of mirror plate, pull-in voltage and eigenfrequency of the micromirror are carried out. The static and dynamic performances of the fabricated micromirror are characterized by Veeco Optical Profiler and Polytek MEMS System Analyzer. The comparison between measurement and simulation exhibits good concordance. Surface topography measurement shows the elevated height and stress-induced concave deformation of mirror plate almost the same scale as demonstrated in FEM simulation. The Pull-In voltages are measured to be around 32V in current-voltage curve which is almost the same as in FEM simulation with one electrode biased. The fundamental resonant frequency is measured to be 4.3k Hz in torsional motion and 4.9k Hz in piston motion.

Hydraulic analysis on effects of back-plate deformation upon stability of high-speed free-surface lithium flow for IFMIF target design

For engineering design of liquid lithium (Li) target of the International Fusion Materials Irradiation Facility (IFMIF), two-dimensional hydraulic analysis was performed using code FLUENT. The analysis clarified effects of smooth deformation at the center of the back-plate part of the flow channel upon velocity and pressure in the high-speed free-surface Li flow. Convex deformations caused decrease in jet thickness and thus increase in velocity and decrease in pressure. Convex deformations caused vice versa. Acceptable limit of the back-plate deformation to avoid Li boiling in IFMIF target was 1.0 mm for the convex deformation and 3.0 mm for the concave deformation. Spatial range of the effects of the deformation was localized around deformation as far as no boiling.

Studies of the deformation styles of the rubber-pad forming process used for manufacturing metallic bipolar plates

Rubber pad forming as a novel stamping technique has been widely used in the deep drawing, bulging, blanking, and flanging processes. It is a feasible method for manufacturing metallic bipolar plates, the surface of which has multi-array flow channels. For a single channel's fabrication, there are two different deformation styles: concave and convex. In this paper, the deformation characteristics of the two deformation styles are analyzed in detail with numerical simulation and experimental methods. The proper application conditions of the concave and convex deformation styles used to fabricate a certain metallic bipolar plate have been determined. If the ratio of the channel width to the rib width w / s > 1 , the concave style is more appropriate; otherwise, the convex style is preferred. Based on this theory, a bipolar plate sample ( w / s < 1 ) is successfully manufactured by the convex rubber-pad forming process.

Simultaneous measurements of velocity and deformation in flows through compliant diaphragms

Flow through a circular orifice in a deformable diaphragm mounted in a pipe was studied experimentally as a simple yet suitable case for validating numerical fluid/structure interaction (FSI) codes including structures with significant deformation and strain. The flow was characterized using pressure taps, particle image velocimetry (PIV), and hot-film anemometry while deformation of the compliant diaphragm was determined directly from PIV images. The diaphragm material properties were measured independently by a uniaxial tensile testing machine. The diaphragm material modulus, orifice diameter, and pipe Reynolds number were varied over ranges appropriate for simulations of flows through heart valves. Pipe Reynolds numbers ranged from 600 (laminar upstream condition) to 8800 (turbulent upstream condition). The pressure drop across the diaphragm resulted in a concave deformation for all cases studied. For the range of Reynolds number tested, the Euler number decreased with increasing Reynolds number as a result of orifice expansion. The flow immediately downstream of compliant diaphragms was jet-like with strong inward radial velocity components and vena contracta. Laminar low Reynolds number flow (Re=600) through both rigid and compliant diaphragms yielded early and regular roll up of coherent vortex rings at a fixed frequency in contrast to turbulent higher Reynolds number flow (Re=3900), which yielded a broad range of vortex passage frequencies. Expansion of the compliant orifice for Re=3900 resulted in an initially broader slower jet with delayed shear layer development compared with the equivalent rigid case.

Analysis of MTJ Edge Deformation Influence on Switching Current Distribution for Next-Generation High-Speed MRAMs

We have demonstrated 500-MHz operation with our high-speed magnetoresistive random access memory (MRAM). For the next-generation MRAM, reducing magnetization switching current and its distribution is very important for decreasing power consumption. We found that some cells showed both large switching current and large switching current distribution under repeated writing tests. Although some failure modes related to the switching current distribution among multiple cells caused by rotated or shifted magnetic properties have been reported, they do not explain the extraordinary properties of each cell. To determine the origin of these properties, we investigated the influence of magnetic tunnel junction (MTJ) edge concave and convex deformation observed in MRAM fabrication. We found that the edge deformation and changed switching process generated a magnetization vortex, causing large switching current in a simulation. The switching characteristics of MTJs with some MTJ edge structures were fabricated and their characteristics were evaluated. We revealed that the edge deformation causes both large switching current and large switching current distribution of each cell. These characteristics correspond with those observed in the MRAM evaluation. Because cell sizes will become smaller and deformation size will become relatively large in the future, controlling MTJ shapes will become increasingly important for developing next-generation MRAMs.

Maturation of the Olfactory Bulbs: MR Imaging Findings

The detection of time-related maturational changes of the olfactory bulb (OB) on MR imaging may help early identification of patients with abnormal OB development and anatomic-based odor-cueing anomalies. Two separate reviewers retrospectively analyzed coronal T2-weighted spin-echo MR images of the frontobasal region in 121 patients. There were 22 patients who underwent MR imaging examinations several times, accounting for a total of 156 studies. Age range was 1 day to 19.6 years. OBs were bilaterally identified in all cases and categorized according to their shape and signal intensity. Three different anatomic patterns were identified. In pattern 1 (median age, 15 days; age range, 1-168 days), the OBs were round to oval with a continuous external T2-hypointense rim and a prominent T2-hyperintense central area. In pattern 2 (median age, 287 days; age range, 4 days-22 months), the OBs were U shaped, with thinning and concave deformation of the superior layer. A hyperintense central area on T2-weighted images was still visible. In pattern 3 (median age, 5.2 years; age range, 107 days-19.6 years), the OBs were small, round, or J shaped with a more prominent lateral part. No difference in signal intensity between the central area and the peripheral layer was identified anymore. The OBs show time-related maturational changes on MR imaging. There is a progressive reorganization of the peripheral neuronal layers and signal intensity changes of the central area, which are completed at the end of the second year, paralleling cerebral maturational changes.

Numerical Simulation of Thixoforging of an AZ91D Magnesium Alloy Magazine Plate and Experimental Validation

In this paper, thixoforging of a magazine plate made of AZ91D magnesium alloy were investigated by means of numerical simulation and experiments. Numerical simulation results show that with increasing punch displacement, local bending, formation of a concave shell part and bulk plastic deformation occurs in billet continuously. Equivalent strain and stress increase and the temperature of the semi-solid billet decreases. When the temperature of the semi-solid billet or the die temperature is elevated, equivalent stain and stress decrease. Optimal technological parameters such as a billet temperature of 545°C, die temperature of 450°C and punch velocity of 15 mm/s were obtained by numerical simulation. Experimental results demonstrate that magazine plates with high mechanical properties such as tensile strength of 316.8 MPa, yield strength of 228.3 MPa and elongation of 12.6 % can be manufactured successfully when the optimal technological parameters selected according to the results of numerical simulation are applied.

Surgical correction of pectus excavatum in two cats

Two sexually intact male Bengal cats, one a 4-month-old weighing 2.8 kg and the other, a 3-month-old weighing 2.0 kg, were presented to the University of Missouri-Columbia Veterinary Teaching Hospital for evaluation of respiratory distress. On initial presentation, both cats were dyspneic, exercise intolerant, and had marked concave deformation of the caudal sternum. Surgical correction of pectus excavatum was performed using a cylindrical external splint and U-shaped external splint. Post-operative thoracic radiography revealed that there was decreased concavity of the sternum and increased thoracic height at the level of the caudal sternebrae in both cats.

Plastic Deformation and Impaction of the Retroacetabular Surface Associated With Posterior Fracture-Dislocation of the Hip: Description of Two Cases

In two cases of posterior fracture-dislocation of the hip, we found an impaction and plastic deformation of the retroacetabular surface, in addition to other typically associated lesions. This deformation creates a mismatch between the stable and the free fragments of the posterior wall, and if unrecognized makes an anatomic reconstruction of the posterior wall impossible. On the computed tomography scan, the most characteristic sign is a concave deformation of the retroacetabular region as compared to the contralateral side. To our knowledge, this specific fracture-dislocation pattern has not been previously described in the literature. If orthopedic surgeons know about the existence of this deformation, then they will easily recognize the impaction on preoperative computed tomography scan and will be able to achieve an anatomic reduction of the acetabulum. Diagnostic aspects and the operative technique to approach this problem are described and illustrated in two cases.

Morphology of compressed dipalmitoyl phosphatidylcholine monolayers investigated by atomic force microscopy

The effectiveness of a substitute of natural lung surfactants on replacement therapy strongly depends on the stability of the monolayer of those substitute molecules. An atomic force microscope is utilized to investigate the microstructure of the films of the major components of natural lung surfactants, dipalmitoyl phosphatidylcholine—DPPC, which are transferred to mica substrates by the Langmuir-Blodgett film technique. A concave deformation structure was first observed for DPPC in solid phase. The depth of the concave domain was about 6 nm and was remarkably uniform. For a collapsed DPPC monolayer, the surface film consists of a granular convex multilayer structure and a disc-like concave structure. Dynamic cyclic compression–expansion experiments indicate that the formation of the concave domain is a reversible process while the process for convex multilayer formation is irreversible. This gives direct evidence that convex grain is the collapsed structure of DPPC monolayer and the concave shallow disc corresponds to the elastic deformation of a DPPC solid film. Results of atomic force microscopy indicate that the nucleation and growth model instead of the fracture model can better describe the collapse behavior of a DPPC monolayer.

An advantage for concavities in shape perception by chimpanzees (Pan troglodytes)

The significance of concavity in object shape perception by chimpanzees (Pan troglodytes) was investigated in a matching-to-sample procedure. For the task, chimpanzees were required to choose a polygon stimulus that was identical in shape to a sample. The incorrect alternative was defined by the addition or subtraction of a concave or convex apex. Chimpanzees were more sensitive to the concave deformation than to the convex deformation. This tendency conforms to the theories of human visual perception that have treated concave features as important factors in reconstructing three-dimensional structures from two-dimensional images. Our results suggest that shape representation in chimpanzees is similar to that in humans and that chimpanzees visually process two-dimensional images in the same manner as humans.