Plastic Hemisphere Research Articles

Failure analysis on abnormal leakage of plastic floating ball in transformer gas relay for nuclear power plant

The plastic components are always more prone to property degradation than the conventional metallic components, so their safety reliability is paid more attention for the routine maintenance. The gas relay containing two plastic balls is an important safety protection device of the high-voltage transformer. The two plastic hollow floating balls inside the relay buoy in the insulating oil level, and float up and down with exhausting and generation of the gas and oil. Once the oil level increases or decreases beyond the safety limits, the protection switches are immediately actuated by the floating ball. In this paper, one plastic floating ball inside the relay in high-voltage transformer was found leaked during one refueling cycle of a nuclear power plant because quite a bit insulating oil was penetrated inside the ball. Although no serious consequence had been aroused, it will bring the potential safety hazards for the normal operation of the transformer. For this reason, the failure analysis was systematically performed to analyze and identify the causes of abnormal leakage of the plastic ball. The comprehensive testing and analysis results indicated that the unqualified fusion process of two plastic hemispheres was the root cause, thus the pertinent countermeasures were proposed.

Thermal stability of piezoelectricity in polylactide polymers and related piezoelectric minimotor application

Piezoelectric polymers have been widely used in a variety of applications, including tactile sensors, energy harvesting, polymer actuators, and biological devices. In this investigation, we fabricated the PLLA (poly(L-lactic Acid)-based bimorph structures for piezoelectric motor applications. First, a strain measurement setup was established to measure the strain of the PLLA and PDLA film at different temperatures. The effective piezoelectric constants d14 calculated for the PLLA and PDLA films were 10.2 pC/N and 9.4 pC/N, respectively. Furthermore, the PLLA films showed a strong thermostability of piezoelectricity at 130°C. The PLLA bimorph minimotor showed the maximum load of 1.2 g and the maximum torque of 0.019 cN·m. The minimotors were capable of rotating a plastic hemisphere container in the clockwise and counterclockwise directions at 65 V voltage. Due to the light weight, low driving voltage, and thermal stability, the PLLA/PDLA motors show a great promise in future Braille display, robots, and mini-digital camera applications.

Research on Elastic-Plastic Contact Behavior of Hemisphere Flattened by a Rigid Flat.

The contact behavior of a hemisphere pressed by a rigid plane is of great significance to the study of friction, wear, and conduction between two rough surfaces. A flattening contact behavior of an elastic–perfectly plastic hemisphere pressed by a rigid flat is researched by using the finite element method in this paper. This behavior, influenced by different elastic moduli, Poisson’s ratios, and yield strengths, is compared and analyzed in a large range of interference values, which have not been considered by previous models. The boundaries of purely elastic, elastic–plastic, and fully plastic deformation regions are given according to the interference, maximum mean contact pressure, Poisson’s ratio, and elastic modulus to yield strength ratio. Then, a new elastic–plastic constitutive model is proposed to predict the contact area and load in the elastic–plastic range. Compared with previous models and experiments, the rationality of the present model is verified. The study can be applied directly to the contact between a single sphere and a plane. In addition, the sphere contact can also be used to simulate the contact of single asperity on rough surfaces, so the present proposed model can be used to further study the contact characteristics of rough surfaces.

Opto-electronic plethysmography: Noninvasive and accurate measurement of the volume of the chest wall and its different thoraco-abdominal compartments

Source of support: None Summary Background: Opto-electronic plethysmography (OEP) is an innovative, new method to evaluate the ventilation pattern through an external measurement of chest wall surface motion. The OEP system measures changes in the complex shape of the chest wall during breathing by modeling the thoracoabdominal surface with a large number of points belonging to selected anatomical reference sites of the rib cage and abdomen. Material/Methods: The automatic motion analyzer on which it is based uses passive markers composed of a thin film of retro-reflective paper on plastic hemispheres (5–10 mm diameter). The markers are placed on the skin by bi-adhesive hypoallergenic tape. Special video cameras (solid state CCDs) operate up to 140 frames per second synchronized with coaxial infrared flashing LEDs. Dedicated software computes the 3D coordinates of the different markers with high accuracy. No specific calibration is required besides the initial one performed during the installation of the system. The OEP System uses the accurate measurement of the 3-dimensional micro-movement of the points belonging to the chest wall to compute chest wall volumes. Special algorithms compute volume variations of the whole chest wall and of the different compartments. Time courses of these signals can be obtained at different sampling frequencies, up to 140 Hz. Results: Several studies have been conducted under different conditions and have shown that the method provides a very accurate measurement of the volume of the chest wall and its variations during respiration. Conclusions: The OEP System has the great advantage that it can measure breathing patterns in any condition, both in health and disease. It can be used to study respiratory kinematics and, if combined with pressure measurements, it can be used to study statics, dynamics, and energetics.

A study of overall contact behavior of an elastic perfectly plastic hemisphere and a rigid plane

The overall contact behavior of an elastic perfectly plastic hemisphere against a rigid plane is presented. Based on volume conservation, the upper limit of overall contact area is derived. A finite element model for the overall contact behavior of a hemisphere and a rigid plane is studied. The material of the hemisphere is assumed to be elastic perfectly plastic. A series of materials with different yield stress to elasticity modulus ratios are studied in finite element analysis. The axial movement of the deformed hemisphere base is prevented. The radial deformable and radial rigid boundary conditions of the hemisphere bottom base are considered. Results show that the overall contact area gradually deviates from Hertz solution, and approaches the upper limit with the increase of interference. Material yield stress to elasticity modulus ratio mainly influences contact behaviors in the early contact stage, while the boundary condition of hemisphere bottom base affects the contact behaviors significantly for large contact interferences. By incorporating some existing models and fitting finite element results, a model for overall contact of a hemisphere against a rigid plane is obtained. This study covers the overall contact, which ranges from initial contact to the collapse of hemisphere. Comparisons of this study with several existing models and experimental data indicate that this study can predict the contact behaviors well in overall contact range.

Creep Relaxation of an Elastic–Perfectly Plastic Hemisphere in Fully Plastic Contact

A set of finite element simulations was performed to analyze the creep behavior of an elastic–perfectly plastic hemisphere in contact with a rigid flat. This study focuses on the time-dependent stress relaxation of a fully plastic asperity. Assuming a Garofalo (hyperbolic sine) type material creep law, the asperity shows two distinct phases of relaxation. In the first phase, the asperity creeps with an accelerated creep rate and shows a contact area increase similar to that of a cylindrical geometry. In the second phase, no contact area change can be measured and the asperity creeps with a slower rate. Empirical evolution laws for the asperity creep behavior are presented, analyzing the influence of both material and geometrical parameters. The results are interpreted in terms of transient friction.

Direct transfer patterning on three dimensionally deformed surfaces at micrometer resolutions and its application to hemispherical focal plane detector arrays

Formation of high performance organic electronic devices on three dimensionally deformed surfaces is severely constrained by the tensile stresses and shear that are introduced during the deformation process. Here, we overcome these limitations to demonstrate the direct transfer of unstrained metals via cold welding onto preformed, 1.0 cm radius plastic hemispheres with micrometer scale feature resolutions to realize 10 kilopixel organic photodetector focal plane arrays (FPAs) that mimic the size, function, and architecture of the human eye. The passive matrix FPA consists of (40 μm) 2 organic double heterojunction photodetectors with response extending across the visible spectrum. The detector dark current density is 5.3 ± 0.2 μA/cm 2 at −1 V bias, and with a peak external quantum efficiency of 12.6 ± 0.3% at a wavelength of 640 nm. The photodetector impulse response was 20 ± 2 ns, making the FPA suitable for video recording applications. The measured dynamic range allows for 7 bit image resolution, and the FPA is used to create a simple image. This demonstration significantly extends the ability to transfer active electronic devices that has previously only been demonstrated on planar substrates.

Lumbosacral orthoses reduce trunk muscle activity in a postural control task

Biomechanical modeling estimated that trunk muscle activity during various tasks could be reduced by 1–14% without the loss of spine stability when a lumbosacral orthosis (LSO) is worn [Cholewicki, J., 2004. The effects of lumbosacral orthoses on spine stability: what changes in EMG can be expected? Journal of Orthopedic Research 22, 1150–1155]. The present study experimentally tested these theoretical predictions in an unstable sitting task. This task required subjects to balance on a seat supported by a plastic hemisphere ( ∅ = 30 cm ) and placed on a force plate that tracked the center of pressure (CoP). The average CoP velocity quantified subjects’ performance. Healthy subjects (12 males, 11 females) balanced for 20 s in 3 trials performed with and without the LSO in random order. EMG was recorded bilaterally from rectus abdominis (RA), external oblique (EO), thoracic (TES) and lumbar erector spinae (LES), and expressed as the % of maximum voluntary activation (%MVA). There was no difference in the balance performance with and without the LSO ( p = 0.13 ) . However, EMG averaged across the trials was significantly lower in the LSO, as compared to the No LSO condition, for TES (5.8±3.2 vs. 6.4±3.7%MVA, p = 0.02 ) and LES (3.7±1.5 vs. 5.9±3.9%MVA, p = 0.01 ). No significant differences were present in the abdominal muscle activity. These results agree with earlier spine modeling simulations, which predicted the greatest reduction in muscle activity due to LSO to occur in TES and LES. It was hypothesized that such a reduction in muscle co-contraction could benefit patients with low back pain, who exhibit elevated muscular activity during postural tasks such as walking, standing and sitting.

Real-Time Opto-Electronic Verification of Patient Position in Breast Cancer Radiotherapy

Objective: The clinical application of an opto-electronic system for real-tune three-dimensional (3D) control of patient position in breast cancer radiotherapy is described. The specific features of the motion analysis technology (shape recognition of passive markers) are detailed, and the outcomes of its clinical use for quantitative position control and immobility verification of the thoracic irradiation field during breast cancer treatment are reported.Materials and Methods: The position control system is based on the ELITEtM opto-electronic motion analyzer, which provides in real time the 3D coordinates of a set of passive markers (plastic hemispheres 3 mm in diameter) previously placed on selected landmarks on the patient's skin. The system-dedicated hardware performs marker recognition by means of 2D correlation of shape with a predefined marker modeling mask. This feature ensures a high accuracy, even with small marker dimensions, and successful analysis in a noisy environment (due to room light, reflexes, etc.). The patient repositioning control was based on a comparison between the current positions of the markers and a corresponding reference configuration. The resulting marker displacements were graphically displayed in real time for immediate control. This information was not provided to the operator as a repositioning tool. Instead, the kinematic data was stored for subsequent off-line analysis aimed at quantifying the different factors contributing to patient mis-positioning (initial repositioning errors, patient's breathing, and random movements) when conventional means for patient alignment (laser centering) and immobilization (casting techniques) are used.Results: Clinical application of the system revealed median 3D localization errors for the directly controlled anatomical landmarks of around 4.5 mm. This value is proposed to represent the intrinsic accuracy of conventional laser-centering techniques in breast cancer radiotherapy, including the effects of patient body deformations. When the positional inaccuracies introduced by patients' respiration were also considered, the extent of the resulting 3D mis-positioning of the control points increased to median values of up to 8 mm.Conclusions: The reported clinical trial confirms the significant role that real-time opto-electronic motion analysis based on passive markers can have in augmenting the accuracy of patient repositioning and immobility verification in the radiotherapy of a non-rigid body area while also accounting for physiological movements. Evaluation of the data collected during each irradiation session for five patients provided valuable information concerning the optimization of the efficacy of traditional methods for patient centering and immobilization.

PS-24-9 Coupling between voluntary tapping, stepping and cardiac rhythms in healthy human subjects

Biomechanical modeling estimated that trunk muscle activity during various tasks could be reduced by 1–14% without the loss of spine stability when a lumbosacral orthosis (LSO) is worn [Cholewicki, J., 2004. The effects of lumbosacral orthoses on spine stability: what changes in EMG can be expected? Journal of Orthopedic Research 22, 1150–1155]. The present study experimentally tested these theoretical predictions in an unstable sitting task. This task required subjects to balance on a seat supported by a plastic hemisphere (∅=30cm) and placed on a force plate that tracked the center of pressure (CoP). The average CoP velocity quantified subjects’ performance. Healthy subjects (12 males, 11 females) balanced for 20 s in 3 trials performed with and without the LSO in random order. EMG was recorded bilaterally from rectus abdominis (RA), external oblique (EO), thoracic (TES) and lumbar erector spinae (LES), and expressed as the % of maximum voluntary activation (%MVA). There was no difference in the balance performance with and without the LSO (p=0.13). However, EMG averaged across the trials was significantly lower in the LSO, as compared to the No LSO condition, for TES (5.8±3.2 vs. 6.4±3.7%MVA, p=0.02) and LES (3.7±1.5 vs. 5.9±3.9%MVA, p=0.01). No significant differences were present in the abdominal muscle activity. These results agree with earlier spine modeling simulations, which predicted the greatest reduction in muscle activity due to LSO to occur in TES and LES. It was hypothesized that such a reduction in muscle co-contraction could benefit patients with low back pain, who exhibit elevated muscular activity during postural tasks such as walking, standing and sitting.

Multifocal corneal topographic changes with excimer laser photorefractive keratectomy.

Excimer laser photorefractive keratectomy can flatten the central cornea, thereby eliminating myopic refractive errors; in older patients, however, presbyopia limits satisfaction. Computer-assisted topographic analysis of corneas after refractive surgery indicates that a minority of patients achieve a multifocal lens effect, such that they maintain reasonable acuity over a range of defocus. We have purposefully attempted to create a multifocal refractive effect and have analyzed the subsequent topographies quantitatively to determine if multifocality was achieved. In corneas not operated on and plastic hemispheres, a fairly small range of corneal powers is observed; the range of powers is increased after a monofocal ablation. After multifocal ablations, a greater spread of surface powers is observed, often with a bimodal distribution, indicative of an apparent multifocal effect. These observations suggest that in some patients undergoing photorefractive keratectomy for myopia, it may be possible to reduce symptoms of presbyopia, although a decrease in image contrast or monocular diplopia may complicate this approach.

Neural grafts attenuate behavioral deficits produced by early radiation-induced hypoplasia of fascia dentata granule cells

Localized X-irradiation of the mitotic cells in the neonatal rat hippocampus produces a discrete hypoplasia of the fascia dentata granule cell layer. This brain damage inhibits the acquisition of a passive avoidance task, and stimulates spontaneous perseverative turning (without reversals) in a plastic hemisphere apparatus. Here we report how transplantation of fetal brain tissue can attenuate these radiation-induced behavioral deficits. The partially shielded cerebral hemispheres of neonatal rats received fractionated exposures to 13 Gray (Gy) of X-rays during the first 16 days post partum. This procedure depleted 90% of the hippocampal granule cells while sparing other brain areas. Control animals were sham irradiated. Baseline behavioral tests were conducted when subjects reached an average age of 147 ± 4 days. We recorded behavioral parameters known to be sensitive to hippocampal damage: (1) passive avoidance performance, and (2) perseverative spontaneous turning without reversals. Irradiated subjects later (average age= 182 ± 4days) received intracerebral transplants of either fetal (E20–21) neurons/neuronal precursors from the fascia dentata or cerebral cortex (control grafts). Additional controls (both irradiated and sham-irradiated) experienced sham surgical procedures or received no surgical manipulation. Two post-surgical behavioral retests were accomplished when rats were 265 ± 5 and 351 ± 6 days old. Rats were then sacrificed and brains were treated histologically to assess radiation-induced brain damage, graft survivability and graft locus. Both hippocampaa and cerebral cortex grafts generally facilitated performance on the passive avoidance task. This effect was most prominent during the first post-surgical test. Hippocampal transplants (especially those found to reside in the damaged hippocampus) also significantly attenuated perseverative spontaneous rotation at the time of the final post-surgical test series. Cortex grafts found within the damaged hippocampus did not ameliorate perseverative movements, while cortex grafts located outside the hippocampus significantly reduced this behavioral deficiency. These data suggest that selected behavioral deficits may be attenuated by transplanting fetal neural tissue long after early radiation-induced brain damage. The success of these procedures depends on a number of factors including: (1) the behaviors chosen for analysis, (2) the time after transplantation that behavioral tests are conducted, and (3) the source and final location of the donor neural tissue.

Progressive behavioral changes during the maturation of rats with early radiation-induced hypoplasia of fascia dentata granule cells

Localized exposure of the neonatal rat brain to X-rays produces neuronal hypoplasia specific to the granule cell layer of the hippocampal dentate gyrus. This brain damage causes locomotor hyperactivity, slowed acquisition of passive avoidance tasks and long bouts of spontaneous turning (without reversals) in a bowl apparatus. Here we report how these behavioral deficits change as a function of subject aging and behavioral test replications. Portions of the neonatal rat cerebral hemispheres were X-irradiated in order to selectively damage the granule cells of the dentate gyrus. The brains of experimental animals received a fractionated dose of X rays (13 Gy total) over postnatal days 1 to 16 and control animals were sham-irradiated. Rats between the ages of 71–462 days were tested 3 separate times on each of the following 3 behavioral tests: 1) spontaneous locomotion, 2) passive avoidance acquisition, and 3) spontaneous circling in a large plastic hemisphere. Rats with radiation-induced damage to the fascia dentata exhibited long bouts of slow turns without reversals. Once they began, irradiated subjects perseverated in turning to an extent significantly greater than sham-irradiated control subjects. This irradiation effect was significant during all test series. Moreover, in time, spontaneous perseverative turning was significantly potentiated in rats with hippocampal damage but increased only slightly in controls. Early radiation exposure produced locomotor hyperactivity in young rats. While activity levels of controls remained fairly stable throughout the course of the experiment, the hyperactivity of the irradiated animals decreased significantly as they matured. The total distance traveled by irradiated rats was significantly above sham-irradiated controls at the beginning of the study but was significantly lower than controls at the conclusion. Young, irradiated rats learned a passive avoidance task more slowly than controls. They not only took more trials to meet criterion but their latency to move into an area in which they had just been shocked was significantly shorter than sham-irradiated rats. Passive avoidance learning improved in mature animals. These data suggest that radiation-induced damage to the fascia dentata produces task-dependent behavioral deficits that change as a function of subject age and/or behavioral testing.

Hyperhemispherical Viewports for Undersea Applications

Hyperhemispherical windows with included spherical angles in the 260–270 degree range have been fabricated from acrylic plastic and glass for a variety of undersea applications. When seated in NOSC rigid metallic mountings with conical seats they withstood cyclic design working pressures without failure, or cracking providing that a thin elastomeric gasket was interposed between the mating conical bearing surfaces, and two elastomeric O-rings served as compliant bushings between the spherical surfaces of the window and the retaining surfaces of the mounting. Tests have shown that (1) critical pressures of acrylic plastic hyperhemispheres can be predicted with acceptable accuracy by analytical and empirical relationships developed previously for acrylic plastic hemispheres and spheres, (2) the mounting retains and seals plastic or glass windows in −40 to 120° F ambient temperature range even when subjected to lateral dynamic loading of 17G magnitude, and (3) dimensionally identical hyperhemispheres fabricated from glass and seated in the same mounting do not fail under a single pressurization at twice the critical pressure of acrylic windows.

Development of Economical Casting Process for NEMO-Type Acrylic Submersible Hulls

This paper describes an improved process for fabricating spherical acrylic plastic pressure hulls within close dimensional tolerances. The process consists of casting acrylic plastic hemispheres in a precision mold assembly, machining their equatorial edge and cutting polar penetrations, bonding them together with a cast-in-place equatorial joint, polishing their inner and outer surfaces, and installing an aluminum hatch and penetration plate. The cost of the improved process is approximately 50 percent less than that of the standard process, which consists of bonding together 12 thermoformed and machined spherical pentagonal shell sections. In addition, 90 percent fewer bonded joints are required, resulting in an order-of-magnitude improvement in optical qualities. A full-scale prototype with an outside diameter of 66.500 in. (168.9 cm) and an inside diameter of 58.000 in. (147.3 cm) has been constructed and shown to be acceptable for manned service to a depth of 2500 ft by hydrostatic testing under sustained loading at pressures of 900, 1350, 1800, and 4000 lb/in.2 (6.2, 9.3, 12.4, 27.6 MPa). Implosion occurred after 13 min of sustained loading at 4000 lb/in.2 (27.6 MPa) and 75°F (23.9°C) simulated depth of 9000 ft (2743 m).

Water Vapour Loss from a Physical Model of a Substomatal Cavity

With the aid of a scale model of a substomatal cavity it has been shown that the rates of evaporation inside such a cavity are greater from loci near the pore than from further away. Implications for the process of evaporation inside a real substomatal cavity are discussed, especially the contribution towards vapour loss from inner epidermal walls. The hypothesis that the water relations of the epidermis should be treated as distinct from those of the leaf as a whole was originally based on evidence of remark ably rapid changes in leaf thickness (mainly epidermal) and stomatal conductance following changes in rates of water supply to, or vapour loss from a leaf (Meidner, 1951, 1965). Added to this was evidence of relatively heavy accumulations in epidermal walls, especially near open stomatal pores, of solutes fed into the transpiration stream (Tanton and Crowdy, 1972 ; Sheriff and Byott, 1976) ; comparatively high hydraulic conductivities of epidermal tissues (Sheriff and Meidner, 1974, 1975); and evapor ation rates from epidermal strips adequate to account for moderate transpiration rates (Meidner, 1975, 1976). As a further test of the hypothesis a physical model of a substomatal cavity was constructed and vapour losses from specific sites within this cavity were determined. MATERIALS AND METHODS Anatomical measurements of substomatal cavities in different leaf species show that in a generalized model of such cavities the dimensions of the different parts might be related to each other as shown in Fig. 1. In this model it has been assumed that the enlarged area of mesophyll cell walls, due to their convoluted shapes, is offset by the long gaseous diffusion paths between the cells so that the inner surface of a hemisphere surmounting a circular flat area can be taken as representative of the cell surfaces supplying water vapour to the substomatal cavity. It should be noted that the flat area, corresponding to inner epidermal walls, accounts for one-third of the total cavity surface in this model. The flat area was made from a 4-mm-thick piece of perspex with a 3-mm-diameter hole drilled in its centre. The plastic hemisphere was sealed on to this plate with a mastic seal. The interior of the assembly was uniformly coated with perspex cement in order to obtain equal properties of ail surfaces. Pieces of filter paper were fitted into the hemisphere and on to the plate ; they were painted on one side and along their edges with na.il varnish so as to make them non absorbent on one side and along their different length margins. One junction of a copper

Flanged Acrylic Plastic Hemispherical Shells for Undersea Application

The effects of an equatorial flange and a nonuniform wall thickness upon the critical pressure and stress distribution in acrylic plastic hemispheres have been investigated by experimental and analytical methods. Forty acrylic hemispheres were fabricated and tested to destruction under short term hydrostatic pressure applied on the convex surface. Dome apex displacements were obtained from each specimen and strains were obtained from a selected few. A finite element elastic analysis was performed on one window configuration for two different boundary conditions and the experimentally derived stresses were used to determine which boundary conditions was the best for analytical analysis.

Organization of the visual projection upon the optic tectum of a reptile (Alligator mississippiensis)

AbstractElectrical responses were recorded from the optic tectum of the alligator with steel microelectrodes, and the receptive field for each of a series of systematically spaced recording sites was delineated on a transparent plastic hemisphere positioned in front of the contralateral eye. A precise retinotopic relationship was determined with the inferior portion of the retina projecting onto the dorsal surface of the tectum, and the superior portion of the retina represented on the lateral and ventral aspects of the tectum. The equatorial line of the hemisphere is situated laterally and runs obliquely across the tectum from the rostrolateral pole to the caudomedial corner. The center of the visual field occupies a disproportionate amount of tectal space providing for functional magnification. Receptive field size and spacing diminish for the representation of the central region implying a retinal area for increased visual acuity. It is suggested that this alinearity between the visual field and the tectum is expressed in its fiber architecture and is probably a consequence of specialization of the eye rather than an evolutionary modification within the reptilian central nervous system.