In situ acoustic characterization of a porous layer backed by a large air cavity

Integrating Monte Carlo calculated dose distributions into an iterative aperture-based IMRT optimization process can improve the final treatment plan. However, the influence of large air cavities in the planning target volume (PTV) on the outcome of the optimization process should not be underestimated. To study this influence, the treatment plan of an ethmoid sinus cancer patient, which has large air cavities included in the PTV, is iteratively optimized in two different situations, namely when the large air cavities are included in the PTV and when these air cavities are excluded from the PTV. Two optimization methods were applied to integrate the Monte Carlo calculated dose distributions into the optimization process, namely the 'Correction–method' and the 'Per Segment–method'. The 'Correction–method' takes the Monte Carlo calculated global dose distribution into account in the optimization process by means of a correction matrix, which is in fact a dose distribution that is equal to the difference between the Monte Carlo calculated global dose distribution and the global dose distribution calculated by a conventional dose calculation algorithm. The 'Per Segment–method' uses directly the Monte Carlo calculated dose distributions of the individual segments in the optimization process. Both methods tend to converge whether or not large air cavities are excluded from the PTV during the optimization process. However, the 'Per Segment–method' performs better than the 'Correction–method' in both situations and the 'Per Segment–method' in the case where the large air cavities are excluded from the PTV leads to a better treatment plan then when these air cavities are included. Therefore we advise to exclude large air cavities and to apply the 'Per Segment–method' to integrate the Monte Carlo dose calculations into an iterative aperture-based optimization process. Nevertheless, the 'Correction–method' provides a good alternative in the case when the external dose engine is not able to generate individual dose distributions for the individual segments.

To determine if different ways in PTV delineation at an air cavity interface yield differences in overall plan quality and treatment efficiency Methods: Three different PTVs were used for treating a patient whose CTV surrounded a large air cavity created by a resected hard palate. The CTV lined the surface of the air cavity while PTV1 included the entire air cavity, PTV2 extended 4mm from the surface of the cavity into air, and PTV3 was reduced 4mm within the surface of the cavity. Tomotherapy plans were generated for all three PTVs. During each planning, all constraints to target and normal structures were kept constant along with the number of optimizations. Same planning process was repeated on a head and neck digital phantom with mock target, normal structures and cavity. Three treatment planning approaches showed no significantly different target coverage in terms of minimum or maximum dose to their respective PTVs. All plans attained 95% coverage of the CTV and PTV by 100% of the prescription. The conformity index (CI) of the plans delivered to PTV1, PTV2, and PTV3 were 1.09, 1.11, and 1.18, respectively. The skin, optic nerves, brainstem and spinal cord all received similar maximum dose to their respective volumes for each plan within 1Gy. The monitor units required for each treatment plan were all within 6% of one another with PTV1 having the highest. For head and neck phantom, the CIs of three plans were 1.05, 1.21, and 1.18, respectively. The coverage of the phantom CTV and sparing of normal structures were nearly equivalent. The total treatment times were identical. Tomotherapy planning is able to deliver dose to a head and neck PTV containing a large air cavity without compromising target coverage, sparing of normal tissues, or delivery time.

An experimental study of cavity and Worthington jet formations caused by a falling sphere into an oil film on water

The cavity walls are a widely used construction system. They became popular in traditional masonry construction for their capacity to reduce the passage of moisture and improve the walls’ thermal performance. However, the latter only applied to narrow cavities with restricted internal air movement. Cavities are also present in emerging technologies, such as 3D concrete printed walls. However, the large cavities of the 3D printed concrete walls have high convective heat transfers that affect the envelope’s thermal performance. Therefore, the authors developed a conjugate heat transfer finite element model to study the large cavities in 3D printed concrete walls and determine the effect on the convective heat transfer of subdividing large cavities. The results show it is possible to reduce the heat flux four times, from 40.4 W/m2 to 9.1 W/m2, subdividing a large cavity into sixteen small ones. This reduction might be higher, increasing the number of cavity subdivisions. However, it is infeasible to restrict the air movements in unfilled air cavities over 25 mm wide for the Rayleigh numbers ≥ 105. Therefore, the practicality of minimizing heat transfer by subdividing large air cavities in 3D printed walls is limited.

Influence of Patient Setup and Target Delineation on Air Cavity Tomotherapy Dosimetry

The aim of the study was to evaluate analysis criteria for the identification of the presence of rectal gas during volumetric modulated arc therapy (VMAT) for prostate cancer patients by using electronic portal imaging device (EPID)-based in vivo dosimetry (IVD). All measurements were performed by determining the cumulative EPID images in an integrated acquisition mode and analyzed using PerFRACTION commercial software. Systematic setup errors were simulated by moving the anthropomorphic phantom in each translational and rotational direction. The inhomogeneity regions were also simulated by the I'mRT phantom attached to the Quasar phantom. The presence of small and large air cavities (12 and 48 cm3) was controlled by moving the Quasar phantom in several timings during VMAT. Sixteen prostate cancer patients received EPID-based IVD during VMAT. In the phantom study, no systematic setup error was detected in the range that can happen in clinical (< 5-mm and < 3 degree). The pass rate of 2% dose difference (DD2%) in small and large air cavities was 98.74% and 79.05%, respectively, in the appearance of the air cavity after irradiation three quarter times. In the clinical study, some fractions caused a sharp decline in the DD2% pass rate. The proportion for DD2% < 90% was 13.4% of all fractions. Rectal gas was confirmed in 11.0% of fractions by acquiring kilo-voltage X-ray images after the treatment. Our results suggest that analysis criteria of 2% dose difference in EPID-based IVD was a suitable method for identification of rectal gas during VMAT for prostate cancer patients.

The behaviour of E24 mild steel, the constituent steel of most moulds for concrete, was studied by voltamperometry and electrochemical impedance spectroscopy in two electrolytes: (i) a filtered cement solution and (ii) a homogeneous mortar without large air cavities. Experiments were carried out with and without Aquadem®, a demoulding agent in aqueous phase. In the filtered cement solution, the E24 steel is passivated and the passivation mechanism is totally controlled by the anodic process, not by oxygen reduction. Whatever the experimental conditions (O2 concentration, rotation speed, immersion time), the corrosion current, i cor, is equal to the anodic plateau current and is of the order of 0.8 μA cm−2. Therefore i cor can be directly assessed from the steady state current–potential curves. The E24 steel in contact with a homogeneous mortar without large air cavities is passivated as well as in the filtered cement solution. For both electrolytes, the results are independent of the presence or absence of Aquadem®. Therefore the pitting corrosion observed in service conditions does not arise from the presence of a solid phase in the electrolyte but may result from the heterogeneity of concrete created by air cavities.

Purpose: To verify the accuracy of the pencil beam algorithm implemented in the FOCUS (CMS) protontreatment planning program with a GEANT4 based Monte Carlo code. Due to the presence of large air cavities and tissue inhomogeneities, paranasal sinus (PNS) cancer brings challenges to radiotherapytreatment planning.Method and Materials: GEANT4 based Monte Carlo methods have been used to simulate multiple PNS cases for the purpose of examining the reliability of the pencil beam algorithm. To guarantee the accuracy of the results by Monte Carlo, the proton treatment nozzle and the patient geometry were modeled in great details, and all related physics processes were included. Different conversion methods for assigning material properties to different Hounsfield units were applied and tested. Electron densities in the Monte Carlo were normalized to the ones used by FOCUS. Results:Monte Carlo and FOCUS present a very good agreement in dose distributions, except for in low‐density air cavities.Monte Carlo reports a significantly lower dose in air than FOCUS, primarily due to a much lower mass stopping power in air than in water. Air cavities, included accidentally in planning contours can cause significant errors in DVHs. With air regions excluded, the DVHs for target structures of Monte Carlo and FOCUS show a good agreement. Differences could be seen in low dose regions and close to material interfaces. However, they are insignificant in most cases. Important, in particular for proton therapy with sharp dose fall‐offs, is the fact that the beam ranges agree very well. Conclusion: This work indicates that the pencil beam algorithm in FOCUS (CMS) is reliable for cases involving large air cavities and bony tissues. However, air cavities should not be included when volumes are drawn for treatment planning.

Measurement of Respiratory Acoustic Signals

This article explores thermal, energy and daylighting performance of double skin facades (DSFs) in different climate types, specifically focusing on three typologies: box window, corridor and multi-story DSFs. These systems were investigated and analyzed to determine how different DSFs perform in comparison to each other, as well as a typical curtain wall (single skin glazed facade used as a baseline), in a multitude of climate applications. The utilized research methods included two-dimensional heat transfer analysis (Finite Element Method analysis), Computational Fluid Dynamics (CFD) analysis, energy modeling, and daylight simulations. Heat transfer analysis was used to determine heat transfer coefficients (U-values) of all analyzed facade types, as well as temperature gradients through the facades for four exterior environmental conditions. CFD analysis investigated three-dimensional heat flow, airflow and air velocity within air cavity of DSFs. Energy modeling and daylight simulations were conducted for an office space, which was enclosed by the analyzed facade types. Individual energy models were developed for each facade type and for fifteen different climates representing various climate zones and subzones, from very hot to arctic. For daylighting simulations, multiple models were developed to study investigated typologies of DSFs, depth of air cavity between the two skins, orientations and four climate types, as well as different sky conditions. Results indicate that there is not a lot of variation in thermal performance of the different DSF types, but that all DSF facades would have significantly improved thermal performance compared to the baseline single skin facade. Energy modeling results indicate significant differences in performance between the DSFs and single skin facade, but fewer variations between the different typologies of investigated DSFs. Moreover, the results show the effect of DSFs in different climate types on energy performance, heating, cooling and lighting loads. Daylighting results indicate that all types of DSFs would decrease daylight levels compared to a conventional curtain wall, however, the differences between lighting levels are also dependent on the orientation, air cavity depth, facade type and climate.

Air cavities employed under ship hulls can result in significant decrease of the water frictional drag by reducing the hull wetted area. However, these cavities usually perform well only in a limited range of the ship speed and attitude. In off-design states and in the presence of sea waves, efficient air cavities covering large areas of the hull are difficult to form and maintain. This problem can be potentially addressed with help of hydrodynamic actuators, such as compact hydrofoils, tabs, and spoilers, which can assist with forming and maintaining air cavities under ship hulls. In this study, exploratory tests have been conducted with a simplistic small-scale hull having a bottom recess. Air was supplied into the recess to produce an air cavity, and several actuators were implemented and manually controlled during the tests. Subjected to external water flow, the air cavity under the hull was found to be responsive to variable positions of the actuators. Positive effects on the air cavity produced with specific actuator settings are identified and discussed in the paper. A series of experimental photographs of the air-water interface are shown for various actuator settings. The air flow rates needed to establish and maintain a large air cavity under the model hull are also reported.

The in situ characterization of materials is a crucial challenge in room acoustics, as laboratories measurement cannot always be applied in consultancy practices. In particular, there is a lack of method to characterize in situ systems with perforated facings, which are commonly encountered systems in room acoustics. In this paper, the in situ characterization of a rigidly-backed porous material behind a rigid perforated facing by means of pressure–velocity measurements is presented. The method includes an inverse impedance model fitting based on measurement in a limited frequency range. The applicability of this method was studied by measuring a variety of perforated facings, whether in front of an air cavity or backed by a porous layer, and comparing the obtained impedance model parameters to reference values. Good agreement was observed between the retrieved parameters and the references, with the errors in all retrieved parameters moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

The main objective of this study is to maximize the rate of sound absorption by applying the parameters of micro-perforated plate (MPP) such as the holes diameter, holes spacing, thickness of MPP, and air cavity depth of MPP. In this study, an optimization algorithm – Firefly algorithm is adopted to determine an optimum set of four parameters for MPP. There are four pieces of MPP with different holes of diameter and spacing was used as specimens. The two-microphone impedance tube method was used to measure sound absorption coefficient (SAC) of MPP sound absorber according to ASTM E1050-12 standard. From the experiments, MPP C (hole diameter = 0.5 mm, hole spacing = 7 mm) for both air cavity depth (30 & 60 mm) score the highest SAC which is 1.00 while MPP B (hole diameter = 0.9 mm, hole spacing = 5 mm) obtain the lowest SAC for air cavity of 30 and 60 mm, which are 0.62 and 0.54 respectively. Then, the firefly algorithm is applied to obtain the optimal solution the set of parameters for MPP sound absorber to reduce the noise level. Hence, it is concluded that by increasing the air cavity depth, holes spacing, and decreasing holes diameter size can increase the rate of sound absorption for MPP. The optimal set of parameters obtained from this study for MPP sound absorber for air cavity, hole diameter and holes spacing are 30, 0.71 mm and 0.5 respectively.KeywordsMicro-Perforated Plate (MPP)Impedance tubeSound Absorption Coefficient (SAC)

The in-situ characterization of acoustic materials is one of the main challenges in room acoustics. Previously, the characterization of a single porous layer backed by a hard wall was successfully done by combining pressure-velocity measurements near the surface of the material with an impedance model fitting approach. In practice however, most porous materials are mounted behind a membrane or a rigid perforated facing. By again combining pressure-velocity measurements and a model fitting procedure, this work studies the possibility to characterize such systems. This was done by measuring a variety of perforated facings and membrane facings, whether in front of an air cavity or backed by a porous layer and comparing the obtained impedance model parameters to the reference values. Good agreement was observed between the retrieved parameters and the references, with error in retrieved moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

The EGS4 Monte Carlo radiation transport code was used to systematically study the dose perturbation near planar and cylindrical air cavities in a water medium irradiated by megavoltage x-ray beams. The variables of the problem included x-ray energy, cavity shape and dimension, and depth of the cavity in water. The Monte Carlo code was initially validated against published measurements and its results were found to agree within 2% with the published measurements. The study results indicate that the dose perturbation is strongly dependent on x-ray energy, field size, depth, and size of cavity in water. For example, the Monte Carlo calculations show dose reductions of 42% and 18% at 0.05 and 2 mm, respectively, beyond the air-water interface distal to the radiation source for a 3 cm thick air slab irradiated by a single 5x5 cm2 15 MV beam. The dose reductions are smaller for a parallel-opposed pair of 5x5 cm2 15 MV x-ray beams, being 21% and 11% for the same depths. The combined set of Monte Carlo calculations showed that the dose reduction near an air cavity is greater for: (a) Smaller x-ray field size, (b) higher x-ray energy, (c) larger air-cavity size, and (d) smaller depth in water where the air cavity is situated. A potential clinical application of these results to the treatment of prostate cancer is discussed.