Search

We report a procedure to design two-dimensional acoustic structures with prescribed scattering properties. The structures are designed from targeted properties in the reciprocal space so that their structure factors, i.e. their scattering patterns under the Born approximation, exactly follow the desired scattering properties for a set of wavelengths. The structures are made of a distribution of rigid circular cross-sectional cylinders embedded in air. We demonstrate the efficiency of the procedure by designing two-dimensional stealth acoustic materials with broadband back-scattering suppression independent of the angle of incidence and equiluminous acoustic materials exhibiting broadband scattering of equal intensity also independent of the angle of incidence. The scattering intensities are described in terms of both single and multiple scattering formalisms, showing excellent agreement with each other, thus validating the scattering properties of each material. [ABSTRACT FROM AUTHOR]

Heat recovery of exhaust gases from main and auxiliary marine diesel engines is an effective way to improve the technical and economic parameters of marine power plants. Improvements in engine efficiency necessitate an increase in the weight-size parameters of the waste heat boilers, which makes it difficult to recover heat. Intensification of the heat transfer process is considered to be an effective way to reduce these indicators. By utilising mathematical modelling, this paper shows the effectiveness of using profiled heating surfaces of waste heat boilers for this purpose. The use of elliptical heating surfaces with a mechanism of controlled flow separation, in the form of a triangular notch, is proposed. This will reduce surface drag and increase the overall thermal-hydraulic efficiency of the heat transfer processes. It is shown that the use of such surfaces in waste heat boilers makes it possible to increase the efficiency of marine power plants in tankers with a deadweight of about 45,500 tons up to 1.5% absolute and container ships with a deadweight of about 122,000 tons up to 2.5% absolute.

Knowledge-based planning (KBP) is a valuable tool for generating plans of consistent quality across planners and institutions. It also provides a training tool for planners new to a treatment planning system. This study assessed the feasibility of implementing KBP for a de-novo linear accelerator (LINAC) with integrated positron emission tomography for biology-guided radiotherapy. The focus of this study was lung SBRT plans due to their greater quantity in the small pool of completed image-guided radiotherapy (IGRT) treatments on our PET/CT-LINAC. To reach sufficient statistical strength in the model training, 50 historical clinical plans of right lung SBRT treatments (50 or 55 Gy, 5 fractions) on our C-arm machines were used to train an in-house developed KBP model using the available tool in a commercial treatment planning system (TPS). External validations (open loop) were performed with 9 clinical C-arm plans to fine tune the model. The C-arm backup plans of three right lung SBRT patients on the PET/CT-LINAC were used to assess the performance of the model. The individually derived KBP templates of the three patients were manually converted into the treatment planning system of the PET/CT-LINAC machine as a starting point for plan optimization and dose calculation. The plans generated in this manner (KBP model-informed plans) were compared with their corresponding clinical plans generated in the same TPS of the PET/CT-LINAC in terms of the dose-volume parameters of planning target volumes (PTV) and organs at risk (OAR). The KBP model-informed plans achieved our clinical goals of acceptable ranges within one round of optimization. Compared to their corresponding clinical plans, the KBP plans showed advantages in dose sparing over general OARs, though some OARs resulted in larger maximum doses. The difference of V20Gy in lungs between the KBP-informed and clinical plans was within ± 1%. The conformity indices of PTVs in the KBP plans were 0.22 ± 0.20 larger on average. The dose of D2cm was generally higher, which is expected since neither 'Ring' structures nor a 'Body-(PTV+2cm)' structure was included in the model. This study demonstrated the capability and utility of a KBP tool in handling the geometric and dosimetric variations in plans that were generated and delivered in a de-novo PET/CT-LINAC system. The KBP-derived planning template for lung SBRT cases was able to generate an initial iteration of clinical plans in the TPS of the PET/CT-LINAC that were within clinical guidelines, particularly for OARs. The sub-optimal performance of target conformity and coverage can be improved in the future by including 'Ring' structures in the model. The preliminary results suggest a promising potential application of KBP in the PET/CT-LINAC system, as more clinical plans of the system become available. Furthermore, this study is also being extended to other treatment sites with more complicated geometries. [ABSTRACT FROM AUTHOR]