Dosimetric Effects of Air Cavities for MRI-Guided Online Adaptive Radiation Therapy (MRgART) of Prostate Bed after Radical Prostatectomy

Purpose: To evaluate dosimetric impact of air cavities and their corresponding electron density correction for 0.35 tesla (T) Magnetic Resonance-guided Online Adaptive Radiation Therapy (MRgART) of prostate bed patients. Methods: Three 0.35 T MRgRT plans (anterior–posterior (AP) beam, AP–PA beams, and clinical intensity modulated radiation therapy (IMRT)) were generated on a prostate bed patient’s (Patient A) planning computed tomography (CT) with artificial rectal air cavities of various sizes (0–3 cm, 0.5 cm increments). Furthermore, two 0.35 T MRgART plans (‘Deformed’ and ‘Override’) were generated on a prostate bed patient’s (Patient B) daily magnetic resonance image (MRI) with artificial rectal air cavities of various sizes (0–3 cm, 0.5 cm increments) and on five prostate bed patient’s (Patient 1–5) daily MRIs (2 MRIs: Fraction A and B) with real air cavities. For each MRgART plan, daily MRI electron density map was obtained by deformable registration with simulation CT. In the ‘Deformed’ plan, a clinical IMRT plan is calculated on the daily MRI with electron density map obtained from deformable registration only. In the ‘Override’ plan, daily MRI and simulation CT air cavities are manually corrected and bulk assigned air and water density on the registered electron density map, respectively. Afterwards, the clinical IMRT plan is calculated. Results: For the MRgRT plans, AP and AP–PA plans’ rectum/rectal wall max dose increased with increasing air cavity size, where the 3 cm air cavity resulted in a 20%/17% and 13%/13% increase, relative to no air cavity, respectively. Clinical IMRT plan was robust to air cavity size, where dose change remained less than 1%. For the MRgART plans, daily MRI electron density maps, obtained from deformable registration with simulation CT, was unable to accurately produce electron densities reflecting the air cavities. However, for the artificial daily MRI air cavities, dosimetric change between ‘Deformed’ and ‘Override’ plan was small (<4%). Similarly, for the real daily MRI air cavities, clinical constraint changes between ‘Deformed’ and ‘Override’ plan was negligible and did not lead to change in clinical decision for adaptive planning except for two fractions. In these fractions, the ‘Override’ plan indicated that the bladder max dose and rectum V35.7 exceeded the constraint, while the ‘Deformed’ plan showed acceptable dose, although the absolute difference was only 0.3 Gy and 0.03 cc, respectively. Conclusion: Clinical 0.35 T IMRT prostate bed plans are dosimetrically robust to air cavities. MRgART air cavity electron density correction shows clinically insignificant change and is not warranted on low-field systems.

Elasticity investigation of thin cellular structure films for piezoelectric sensors

Purpose This paper aims to present the details of isotactic polypropylene (it-PP) films with a cellular structure (air-cavities) dedicated to pressure sensors. The polymer composites (thin films enriched with 5 and 10 wt% of mineral fillers as Sillikolloid P 87 and glass beads) should exhibit suitable structural elasticity within specific stress ranges. After the deformation force is removed, the sensor material must completely restore its original shape and size. Design/methodology/approach Estimating the stiffness tensor element (C33) for polymer films (nonpolar space-charge electrets) by broadband resonance ultrasound spectroscopy is a relatively simple method of determining the safe stress range generated in thin pressure sensors. Therefore, ultrasonic and piezoelectric studies were carried out on four composite it-PP films. First, the longitudinal velocity (vL) of ultrasonic waves passing through the it-PP film in the z-direction (thickness) was evaluated from the ω-position of mechanical resonance of the so-called insertion loss function. In turn, the d33 coefficient was calculated from accumulated piezoelectric charge density response to mechanical stress. Findings Research is at an early stage; however, it can be seen that the mechanical orientation of the it-PP film improves its piezoelectric properties. Moreover, the three-year electric charge stability of the it-PP film seems promising. Originality/value Ultrasonic spectroscopy can be successfully handled as a validation method in the small-lot production of polymer films with the air-cavities structure intended for pressure sensors. The structural repeatability of polymer films is strongly related to a homogeneous distribution of the electric charge on the electret surface.

STATIC CONTROL OF DRAG-REDUCING AIR CAVITIES WITH VARIABLE CAVITATOR SHAPE

Air ventilation of submerged surfaces of ship hulls is a promising technique for drag reduction. To ensure high performance of air cavities in a broad range of operational conditions, the cavity properties can be controlled with help of compact hydrodynamic actuators. In this study, a potential flow theory is applied to model an air cavity formed behind a wedge-shaped cavitator under a horizontal wall imitating a ship bottom. By varying the wedge angle, it is possible to achieve states with maximum drag reduction at given operational conditions. The dependence of the optimal wedge angle on Froude number and hull trim is investigated. The air-cavity ability to reduce frictional drag is found to increase with rising flow speed and bow-down hull trim.

Hydrodynamics and Warmth Trade in Cycles of Cooling of an Attractive Plate in an Attractive Fluid in the Attractive Field

The effect of the magnetic field on heat transfer processes of a magnetized steel plate cooled in a magnetic fluid is experimentally studied. Thermocouples were installed at six points on the surface of the plate along its length. The plots of temperature versus time are obtained in the absence of a magnetic field and in magnetic fields of different intensity. It is found that the intensity of heat exchange depends to a large extent on the magnitude of the magnetic field and on the location of points on the surface of the plate. In a magnetic field, cooling of the central part of the plate occurs with the same intensity as in the absence of a magnetic field and with a lower intensity in comparison with other points on the surface of the plate. Near the plate ends, the cooling rate of the surface is much greater in the magnetic field than in the absence of it. With increasing magnetic field strength, the cooling rate of points in the central part of the plate decreases and is less than in the absence of a magnetic field. The dependence of heat transfer on the magnitude of the magnetic field is explained by the distribution of the magnetic forces acting on the liquid surrounding the plate and the nature of the vapor-air cavities formed near its surface. Experiments on simulation of formation and the shape of vapor-air cavities in a liquid surrounding a magnetizing plate are described.

Using CFD modelling to study hydraulic flow over labyrinth weirs

Compound labyrinth weir is a new type of labyrinth weirs that consider a good applicable choice for increasing the capacity of discharge. The flow over a compound labyrinth weirs is a complex problem because the flow behavior is three-dimension. The present study aims to simulate the flow over the compound labyrinth weir into the critical regions that can not be observed when using an experimental test. The computational fluid dynamics (CFD) programme was utilised to implement a sensitive analysis for this purpose and different flow conditions. The MAPE and RMSE indices were utilised to verify the CFD results with experimental work. The statistics indices of the maximum error ME, RMSE and MAPE were 4.7%, 0.033 and 3.9 respectively. Therefore, the findings showed that there is a good matching between the experimental and CFD results. The CFD results demonstrated that the hydraulics behaviour of the compound labyrinth weir was similar to the oblique and linear weirs in high discharges. The results also confirmed that air cavities and bubbles existed behind the nappe flow in addition to the negative pressure that may occur beneath the nappe when the flow is aerated. Furthermore, the flow was divided into two parts and most streamlines were concentrated over the notches. Moreover, the flow velocity passing through the notches was bigger than the flow velocity over the high crest of the compound labyrinth weir.

Bubble production by air filament and cavity breakup in plunging breaking wave crests

Air filaments and cavities in plunging breaking waves, generically cylinders, produce bubbles through an interface instability. The effects of gravity, surface tension and surface curvature on cylinder breakup are explored. A generalized dispersion relation is obtained that spans the Rayleigh–Taylor and Plateau–Rayleigh instabilities as cylinder radius varies. The analysis provides insight into the role of surface tension in the formation of bubbles from filaments and cavities. Small filaments break up into bubbles through a Plateau–Rayleigh instability driven through the action of surface tension. Large air cavities produce bubbles through a Rayleigh–Taylor instability driven by gravity and moderated by surface tension, which has a stabilizing effect. Surface tension, interface curvature and gravity are all important for cases between these two extremes. Predicted unstable mode wavenumber and bubble size show good agreement with direct numerical simulations of plunging breaking waves and air cylinders.

Recent progress of SPIDER: Aspects of subtractive approaches to existing building’s performance improvement

This contribution reports about methodology, progress and preliminary findings of a recent exploratory Research and Development project, pertaining to the (semi-)automated thermal retrofit of existing building’s envelopes. Thereby, the potential of robots, which autonomously identify areas of facades that can be used for inserting openings into the existing wall material, is examined. The idea is based on the fact that masonry walls of historic masonry walls (especially of Gründerzeit buildings built between 1850 and 1918) often have been structurally over-dimensioned. As such, the spare thickness of the walls could be used for thermal insulation purposes. The initial idea to implement air cavities for insulation purposes is in correspondence with the predominant functional principle of most insulation materials.