Influence Of Air Gap Research Articles

Influence of Air Gap under Bolus in the Dosimetry of a Clinical 6 MV Photon Beam.

Aim:In some situations of radiotherapy treatments requiring application of tissue-equivalent bolus material (e.g., gel bolus), due to material's rigid/semi-rigid nature, undesirable air gaps may occur beneath it because of irregularity of body surface. The purpose of this study was to evaluate the dosimetric parameters such as surface dose (Ds), depth of dose maximum (dmax), and depth dose along central axis derived from the percentage depth dose (PDD) curve of a 6 MV clinical photon beam in the presence of air gaps between the gel bolus and the treatment surface.Materials and Methods:A bolus holder was designed to hold the gel bolus sheet to create an air gap between the bolus and the radiation field analyzer's (RFA-300) water surface. PDD curves were taken for field sizes of 5 cm × 5 cm, 10 cm × 10 cm, 15 cm × 15 cm, 20 cm × 20 cm, and 25 cm × 25 cm, with different thicknesses of gel bolus (0.5, 1.0, and 1.5 cm) and air gap (from 0.0 to 3.0 cm), using a compact ionization chamber (CC13) with RFA-300 keeping 100 cm source-to-surface (water) distance. The dosimetric parameters, for example, “Ds,“ “dmax,“ and difference of PDD (maximum air gap vs. nil air gap), were analyzed from the obtained PDD curves.Results:Compared to ideal conditions of full contact of bolus with water surface, it has been found that there is a reduction in “Ds“ ranging from 14.8% to 3.2%, 14.9% to 1.1%, and 12.6% to 0.7% with the increase of field size for 0.5, 1.0, and 1.5 cm thickness of gel boluses, respectively, for maximum air gap. The “dmax“ shows a trend of moving away from the treatment surface, and the maximum shift was observed for smaller field size with thicker bolus and greater air gap. The effect of air gap on PDD is minimal (≤1%) beyond 0.4 cm depth for all bolus thicknesses and field sizes except for 5 cm × 5 cm with 1.5 cm bolus thickness.Conclusions:The measured data can be used to predict the probable effect on therapeutic outcome due to the presence of inevitable air gaps between the bolus and the treatment surface.

Investigation of NdFeB N52 magnet field as advanced material at air gap of axial electrical generator

The aim of this study is to investigate and analyze the NdFeB N52 type magnetic field distribution on a Trapezoidal type coil in an axial type generator. The main problems addressed by this study are how the distribution of magnetic field type NdFeB N52 to the trapezoidal type coil and how the influence of air gap between NdFeB N52 magnets and the coil to the output electric voltage generated from the coil at the speed of rotation. In order to answer the problems, we moved a rectangular type magnet axially towards the trapezoidal type coil with a specified distance, so that we could identify the change of the output voltage. The description of the magnetic field distribution in the stator was simulated by using the Maxwell 3D Design application ran in ANSYS software 16.0. The result of this study shows that the magnet was distributed evenly on the coil. It is also known that based on experiments with 2mm to 6mm of magnet to coils of gaps, the highest output voltage is at 2mm gaps at 750rpm.

P213] Influence of beam spoiler and air gap on dose distribution in build-up region for X6 MV static field

Purpose Basing on CBCT images we noticed, that there are several different problems with reproducibility of bolus positioning, especially air gap occurrence. The aim of this study was to determine the influence of air gaps between bolus and phantom on dose distribution in build-up region for X6 MV. The novelty of the work is using low-density boluses fabricated with 3D printer. Methods Depth dose measurements were performed for X6 MV 10×10 cm2 open field, generated with Varian CL 2300 C/D. The measurements were carried out with the Markus plane parallel ionization chamber (PTW, 0.055 cm3 volume), connected to Unidos (PTW) electrometer. As 1 cm thick beam spoilers we used 3D-printed thermoplastic polyurethane (TPU) cuboids filled with 5%, 10%, 15% and 20% honeycomb structure (thickness of 0.5 g/cm2; 0.17 g/cm2; 0.22 g/cm2). To generate air gap we used homemade styrofoam frames. Measurements were performed at a physical depth of 1, 5, 10 and 15 mm for all beam spoilers without air gaps and with 10, 20, 30 and 40 mm air gaps, at constant 90 cm SSD. Results Our results showed that beam spoilers without air gap increased the dose in build-up region. The bigger spoiler filling is, the larger is surface dose. The same dependence can be seen on Percentage Depth-Dose curves, irrespectively of air gap size. Regardless of spoiler percentage filling with honeycomb structure, the larger air gap size is, the smaller dose on 1 mm depth. Conclusions Influence of beam spoiler filling and air gap on dose distribution in build-up region for X6 MV was investigated. Beam spoiler increased the dose in build-up region. The larger thickness of beam spoiler (larger filling) - the larger influence on build-up dose. Occurrence of air gaps lowers the surface dose. However, the influence of air gap in the range of 10–40 mm is not very visible. For bolus with density of 0.22 g/cm2; regardless of air gap size, the dose on 1 mm depth was always larger than 95% of maximum dose. The issue will be investigated for wedged and dynamic fields.

Numerical Study of Temperature Distribution Control in Precision Glass Molding Furnace

In a precision glass molding process, glass preform is compressed at a high temperature well above its transition temperature and the temperature distribution inside plays an important role in determining the quality of final products. In this research, a 2D axisymmetric numerical heat transfer model, integrated with an innovative PID control subroutine, was employed for simulating the temperature control process and obtaining transient temperature distribution in the glass preform. Feasibility of this method was validated by experiments with good agreements. Finally, influence of air gap between glass preform and upper mold as well as temperature control mode were investigated. The results showed that temperature difference of the molds had a severer influence on the temperature distribution of glass preform with the decrease of air gap. In addition, a two-point control strategy was demonstrated as a valid method to improve the temperature uniformity in the glass preform.

Empirical flashover model of EHV post insulators based on ISP parameter in cold environments

The main objective of this contribution is to present an empirical model of ice-covered insulator flashover in accordance with an important flashover index, called icing stress product (ISP). The ISP as the product of the ice mass per centimeter of insulator length and the electrical conductivity of the melted ice accretion is used to establish an empirical model to determine the flashover voltage under icing conditions. To achieve this model, several tests were carried out on post station insulators typically used in Hydro-Quebec 735-kV substations, under DC and AC voltage, to determine the relationship between flashover stress and the ISP. The ISP-based method offers a good tool not only to select insulators for locations exposed to freezing conditions, but also to compare flashover results obtained under different test conditions. Moreover, to study the optimizing method of insulator flashover, the influence of air gaps on the flashover stress of ice-covered post insulators is investigated. The results reveal that the number of air gaps significantly affects the flashover stress. The test results are highly meaningful as they can be used as a reference for ranking several other insulator types and configurations in order to select the appropriate one for cold environments. Moreover, several mitigation options to improve insulator reliability in cold environments are provided.

Influence of air Gap Between the Transformer of Resistance and Object of Monitoring on Temperature Measurement Error

In operation the description of the developed heattransfer model in thermotransformers of resistance (RTD) in the conditions of air gap between surfaces of the sensor and object of measurement is provided. Research of influence of thickness of air gap on the relative error of temperature measurement by platinum, copper and nickel thermotransformers of resistance in the ranges of temperatures corresponding to each type is executed. Dependences of minimum necessary duration of heating up of sensors on the taken temperatures are received.

A Preliminary Study on Acoustical Performance of Oil Palm Mesocarp Natural Fiber

As the population increases, the demand of a comfortable environmental such as sound pollution is getting higher. Sound pollutions also have become worsen and creating concerns for many peoples. Due to this problem, synthetic materials as acoustic absorbers still applied as commonly acoustical panels and this material may hazardous to human health and contribute significantly a pollution to the environments. However, researchers have interested in conducting their research on natural fiber to be an alternative sound absorber. This study investigated the potential of oil palm Mesocarp fiber for sound absorbing material. The Mesocarp fibers were mixed with polyurethane (PU) as binder with ratio of 70:30. The thickness was varied in 10mm, 20mm, 30mm, and 40mm. This study also investigated the air gap of 5mm and 10mm in the sound absorption performance. Impedance Tube Method was used to measure sound absorption coefficient (a). The measurement was done on accordance with ASTM E1050-98, which is the standard test method for impedance and absorption of acoustical materials using a tube. The results showed that the optimum value for Mesocarp fiber is 0.93. The optimum value obtained at 5000 Hz. The influence of air gap increases the sound absorption especially from 250 Hz to 4000 Hz. These results indicate that fiber from Mesocarp is promising to be used sound absorbing material.

Electrical performance evaluation of EHV post insulators covered with ice under different air gap configurations

This paper investigates the influence of air gaps on the maximum AC withstand voltage (VWS) of ice-covered post insulators, typically used in Hydro-Quebec 735-kV substations. The VWS was experimentally determined based on IEEE Standard 1783, under icing conditions. The results reveal that the number of air gaps affects the VWS significantly. The configuration with four air gaps allows improving the VWS by 15% in comparison to the configuration with three air gaps. Moreover, high speed video camera techniques were used to observe the mechanism of electric arc propagation over ice surface with respect to the air gap configuration. Also, to interpret the performance of the ice-covered insulators with different air gap positions, the voltage and electric field distributions along the ice-covered insulator were simulated numerically by the Finite Element Method (FEM) during the melting period. The simulation results confirmed that increasing the number of air gaps improves satisfactory the uniformity of voltage distribution of the EHV post insulators and consequently the maximum withstand voltage. Based on the obtained results, the installation of booster sheds to improve the insulating performance of post insulators under icing conditions was recommended.

Preparation and characterization of α-Al2O3 hollow fiber membranes with four-channel configuration

Four-channel α-Al2O3 ceramic hollow fibers were first fabricated by a combined phase-inversion and sintering technique. The hollow fibers could provide low transport resistance as well as high mechanical strength. Influences of air gap and sintering temperature on properties of the obtained hollow fibers were investigated. Using an air gap of 100mm and a sintering temperature of 1450°C for 5h, the as-prepared four-channel fibers with the cross-linking configuration showed a pure water flux of 1.93m3m−2h−1 at 0.1MPa and a fracture load of 18.5N, which was superior to that of single-channel ceramic hollow fiber. It is suggested that the four-channel ceramic hollow fibers exhibit great potential for practical applications.

Hot Stamping of Two Different High Strength Steel with Tailored Properties

With the increasingly widespread application of high-strength steel (HSS), tailored properties, namely different mechanical properties required in different regions of the same part, have been proposed, in order to achieve the matching between mechanical properties and safety performance of motor vehicle parts. In this paper, the influence of air gap on the final hardness and strength distribution is discussed in terms of two different HSS, namely LG1500HS and WHT1500HF. As for steel LG1500HS, regardless of the location of samples in the formed part, the final fracture area is in the vicinity of the air gap center, proving the lowest hardness and strength in transition zones. Compared to steel LG1500HS, steel WHT1500HF exhibits gradient hardness distribution from the cooling zone to the heating zone, with no minimal value discovered in transition zones.

Modeling Analysis and Parameters Calculation of Permanent Magnet Linear Synchronous Motor

Permanent magnet linear synchronous motor (PMLSM) has several advantages, such as simple structure, small volume, high force, and so on. It is a research focus and difficulties in the research field of motor. Because PMLSM is different from the traditional rotary motors in structure and running state, it is difficult for to build its precise mathematical model by analytical method. The asymmetry of the three-phase winding electromagnetic and electrical parameters of open PMLSM in a low-speed working zone is impossible to take into account. In this paper, the difference between the permanent magnet linear synchronous motor and traditional motors are analyzed. And then, a non-linear, asymmetric and variable parameter space state model is built, considering the structural and running characteristics of PMLSM. The proposed model needs all kinds of parameters of PMLSM, including self- inductance, mutual inductance, flux linkage, etc. So, a finite element calculation and actual measurement of the required parameters of a prototype PMLSM are done, respectively. The influence of air-gap on the inductance parameters was analyzed.

Development of Dynamic Loading Device for Rotating Spindle of Machine Tools

High performance milling spindles, which have high rigidity and high speed, are required for high productive machining. In order to evaluate the rigidity change of the spindle, authors has been developed a magnetic loading device. This device provides attractive force in radial direction to a dummy tool attached to a spindle. By using this device, the static stiffness of the rotating spindle has been successfully evaluated. However the loading rate could not be controlled due to the electric response lag caused by the magnetic field. To solve this problem, electric response of the coil-tool system with the air gap is analyzed and the dynamic response is estimated. The air-gap's influence on the load was also evaluated. Based on the analysis, a dynamic loading test is designed carried out for the measurement of the rigidity of a machine tool spindle.

Study on the Magnetic Flux Leakage (MFL) for Fillet Weld

The magnetic flux leakage (MFL) technique is widely used as a Non-Destructive Testing (NDT) method for welds [1]. Because of the specialty of fillet weld structure, the defect may not be in the location suitably detected, which is normally at the center of yoke poles, and the rate of detect-ability would decline. In this paper, we focus on the yoke-magnetization testing for a fillet weld, and it is studied the influences of air gap between magnetic poles and specimen surface on MFL density at an artificial flaw by Finite Element Method (FEM), and also the influences of distance between magnetic poles and fillet weld on MFL density. The results show that the MFL density observably decreases as the air gap and the distance increase.

Space State Modeling of Permanent Magnet Linear Synchronous Motor and Inductance Parameters Calculation

Different from the traditional rotary motors in structure and running state, it is difficult for permanent magnet linear synchronous motor (PMLSM) to build its precise mathematical model by analytical method and the asymmetry of the three-phase winding electromagnetic and electrical parameters of open PMLSM in a low-speed working zone is impossible to take into account. In this paper, considering the structural and running characteristics of PMLSM, a non-linear, asymmetric and variable parameter space state model is built. Then a finite element calculation and actual measurement of the required inductor values of a space state model with a prototype PMLSM are done respectively, and the influence of air-gap on the inductance parameters is analyzed.

Influence of air gaps on the thermal–electrical–mechanical behavior of a copper metallization

Shrinking the IC dimensions the dielectric insulation between metal interconnects has become one of the major limits on increasing circuit speed. A lot of possible new low-k materials failed to meet specifications: too leaky, too soft, too unstable, and too expensive. Due to this air gaps beside the metallization are one solution. The reliability of ULSI multilevel copper metallizations under electro- and stress migration stress test conditions is investigated here with finite element analysis. A determination of the electrical and mechanical stress in a 3D copper metallization model based on the 45nm technology node is carried out and the impact of a variation of the applied current density as well as geometrical parameters on the thermal–electrical and mechanical behavior is investigated. For a determination of the reliability the mass flux and mass flux divergence are separately calculated by a user routine. The influence of air gaps on single via structures and structures with a chain of four vias on the thermal–electrical–mechanical behavior is determined.

Analyzing stored thermal energy and thermal protective performance of clothing

Protective clothing can store large amounts of energy when exposed to thermal (heat, flame) hazards. After exposure, the stored thermal energy discharges naturally—or may be forced if the clothing is compressed suddenly—and contributes to human skin burn injuries. In this study, the stored thermal energy that develops in thermal protective clothing materials was analyzed under different conditions. A stored energy approach that accounts for the thermal energy contained in the exposed test specimen is developed. The stored energy approach measures the total energy delivered to the sensor from a combination of the energy directly transmitted during exposure and the energy stored in the fabric system that is subsequently discharged after the thermal exposure. The study examines the effects of moisture on protective performance and the influence of air gaps between the fabrics and the sensor in terms of a stored energy approach and TPP/RPP (thermal protective performance/radiant protective performance) approach. A minimum exposure time that caused a prediction of a second degree burn was introduced and its contribution to burn injury was examined. These analyses demonstrate that the stored thermal energy obtained during thermal exposure is significant for multilayer protective clothing. Stored thermal energy contributes a large part of the total energy required to cause a second degree skin burn injury. The results indicate that, in cases of thermal exposure, stored thermal energy can reduce significantly the level of protection expected from wearing protective clothing.

Use of a hybrid adaptive finite element/modal approach to assess the sound absorption of porous materials with meso-heterogeneities

The paper discusses the sound absorptive performance of a porous material with meso-perforations inserted in a rectangular waveguide using a numerical hybrid adaptive finite element-modal method. Two specific applications are investigated: (i) the improvement of porous materials noise reduction coefficient using meso-perforations (ii) the effects of lateral air gaps on the normal incidence sound absorption of mono-layer and two-layer porous materials. For the first application, a numerical design of experiments is used to optimize the sound performance of a porous material with meso-perforations with a reduced number of numerical simulation. An example in which the optimization process is carried out on the thickness and size of the perforation is presented to illustrate the relevance of the approach. For the second application, a set of twenty fibrous materials spanning a large flow resistivity range is used. Practical charts are proposed to evaluate the influence of air gaps on the average sound absorption performance of porous materials. This is helpful to both the experimenter regarding characterization of porous material based on Standing Wave Tube measurements and for the engineer to quantifying the impact of air gaps and for designing efficient absorbers.

Analysis of a Permanent-Magnet Brushless DC Motor with Fixed Dimensions

Analysis of a Permanent-Magnet Brushless DC Motor with Fixed DimensionsThe purpose of this paper is to describe the analysis of a permanent-magnet brushless DC motor with fixed outer diameter and active zone length. The influence of air gap, material of permanent magnets and their size on the magnetic flux density of the machine and magnetic flux is analyzed. The work presents the calculations of two programs, the comparison of the results and the most suitable combination of factors that has been found.

WE‐C‐224C‐06: Influence of Air Gap On Dosimetric Characteristics of Uniform and Composite Clinical 90Y Plaques for Dural Irradiation

Purpose: A semi‐cylindrical polycarbonate plaque incorporating a 90Y foil has been developed and used to irradiate the dura in 14 spinal tumor patients. It has been hypothesized that inadequate fitting of the irradiator plaque to the dural surface could adversely affect the area of therapeutic dose delivery at the 90% level. A differentially‐loaded composite treatment plaque has been designed to ameliorate potential air gap effects and maximize therapeutic dose delivery. Method and Materials: Two clinical plaque designs were evaluated, including a “standard” plaque containing a single foil of uniform activity, and a “composite” plaque containing a differentially‐loaded 90Y source created by placing a single activated square foil under an activated foil frame of the same outer dimensions in a titanium shell. Two dosimetry phantoms surrounded by a layer of radiochromic film (GafChromic HS) were constructed with radii approximating a perfect fit (matched to inner plaque radius) and a gap fit (80% of inner plaque radius) and irradiated with the two plaques. Results: Analysis of the irradiated film demonstrated that the effective treatment width to 90% of the plaque along the arc in the standard plaque is 65.8% when fitted and 58.1% in the presence of a gap; for the composite plaque, the corresponding treatment widths to 90% are 88.6% when fitted and 69.4% in the presence of a gap. Thus, in the presence of a gap the composite plaque delivers dose at the 90% level to a 19.6% greater arc width than the standard plaque with a gap, and 5.5% greater arc width than a perfectly fitted standard plaque. Conclusion: Differentially‐loaded composite 90Y plaques deliver therapeutic dose to a substantially larger treatment area than standard plaques currently used, and completely resolve treatment area to the 90% level potentially lost to inadequate fit with standard plaques.

Analysis of out-of-plane thermal microactuators

Out-of-plane thermal microactuators find applications in optical switches to motivate micromirrors. Accurate analysis of such actuators is beneficial for improving existing designs and constructing more energy efficient actuators. However, the analysis is complicated by the nonlinear deformation of the thermal actuators along with temperature-dependent properties of polysilicon. This paper describes the development, modeling issues and results of a three-dimensional multiphysics nonlinear finite element model of surface micromachined out-of-plane thermal actuators. The model includes conductive and convective cooling effects and takes into account the effect of variable air gap on the response of the actuator. The model is implemented to investigate the characteristics of two diverse MUMPs fabricated out-of-plane thermal actuators. Reasonable agreement is observed between simulated and measured results for the model that considers the influence of air gap on actuator response. The usefulness of the model is demonstrated by implementing it to observe the effect of actuator geometry variation on steady-state deflection response.