Селективный магнитный контроль толщины и степени упрочнения поверхностных слоев на стальных объектах

The dependences of measured locally magnetic characteristics of surface-hardened steel objects on the thickness and physical properties of their surface layers are studied. It is shown theoretically and experimentally that a change in the thickness of the hardened layer on the surface of steel objects affects on the magnitude of the tangential field component on the surface of the object in the interpolar space significantly , as well as the change in the strength properties of the layer affects the magnitude of the magnetic flux in the "transducer-object" circuit. It is proposed to use this difference in magnetic parameters for selective testing of the surface hardening quality. It is shown that the coercive force measured locally by the internal field and the maximum value of the magnetic flux, which can be measured using a single transducer in single measuring cycle, can be used as diagnostic parameters.

Heart atlas for retrospective cardiac dosimetry: a multi-institutional study on interobserver contouring variations and their dosimetric impact

Purpose Cardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart’s heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies. Methods and materials The atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability. Results Contouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement. Conclusions For the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.

Recent advances in bianisotropic boundary conditions: theory, capabilities, realizations, and applications

In recent years, new functionality and unprecedented wavefront control has been enabled by the introduction of bianisotropic metasurfaces. A bianisotropic metasurface is characterized by an electric response, a magnetic response, and an electro-magnetic/magneto-electric response. In general, these metasurfaces consists of an array of metallic or dielectric particles located within a subwavelength thick host medium, and are approximated and modeled as infinitely-thin, idealized sheet boundaries defined along a surface. An appropriate sheet boundary condition which effectively models the tangential field discontinuity due to the array of magnetoelectric inclusions is the Generalized Sheet Transition Condition or GSTC. Several forms of the GSTC appear in literature. Here, we present each interpretation and show how they are related. Synthesis approaches unique to each form are overviewed. By utilizing the GSTC in metasurface design, new possibilities emerge which are not possible with conventional design techniques incorporating only electric or only magnetic responses. Since the metasurfaces are designed using bianisotropic boundary conditions, they must be realized using particles which contain magnetoelectric responses. This review article discusses the design of metasurfaces using the GSTC, and the bianisotropic particles used to realize GSTC’s. Further, it discusses new and recent applications that have emerged due to bianisotropy, and future prospects in metasurface design using bianisotropic boundary conditions. The intent is to provide a comprehensive overview of metasurface design involving bianisotropy and for this review article to serve as a starting point for engineers and scientist that wish to introduce bianisotropy into metasurface design.

Electric Field Distribution in HVDC Cable Joint in Non-Stationary Conditions

Accessories such as joints and terminations represent weak points in HVDC cable systems. The DC field distribution is intimately dependent on the thermal conditions of the accessory and on material properties. Moreover, there is no available method to probe charge distribution in these conditions. In this work, the field distribution in non-stationary conditions, both thermally and electrically, is computed considering crosslinked polyethylene (XLPE) as cable insulation and different insulating materials (silicone, rubber, XLPE) for a 200 kV joint assembled in a same geometry. In the conditions used, i.e., temperatures up to 70 °C, and with the material properties considered, the dielectric time constant appears of the same order or longer than the thermal one and is of several hours. This indicates that both physical phenomena need to be considered for modelling the electric field distribution. Both the radial and the tangential field distributions are analysed, and focus is given on the field distribution under the stress cone on the ground side and near the central deflector on the high voltage side of the joint. We show that the position of the maximum field varies in time in a way that is not easy to anticipate. Under the cone, the smallest tangential field is obtained with the joint insulating material having the highest electrical conductivity. This results from a shift of the field towards the cable insulation in which the geometrical features produce a weaker axial component of the field. At the level of the central deflector, it is clear that the tangential field is higher when the mismatch between the conductivity of the two insulations is larger. In addition, the field grows as a function of time under stress. This work shows the need of precise data on materials conductivity and the need of probing field distribution in 3D.

Improvement of matching fields using coplanar field border method in postmastectomy radiotherapy

Aim: To propose a new matching method for the supraclavicular (SC) and tangential fields on three-dimensional radiotherapy (3DRT) for postmastectomy radiotherapy (PMRT). Methods: A method of matching coplanar field borders (CFB) between the tangential and SC fields was created in 3DRT. The collimator angle of the medial tangential field was calculated to coplanar the SC field. The proposed method performance was ultimately benchmarked using the half beam block (HBB) and traditional three-field monoisocenter (TTM) methods by dosimetric comparison. The decision score was then employed to clarify the performance among these methods. Results: The results show that the TTM method exhibited not only low doses on the organs at risk (OAR) but also on the matching fields. The CFB and HBB produced comparable results, but the ipsilateral lung yielded lesser amounts than the HBB. The decision score indicated a low performance level when using the TTM method, whereas the CBF method exhibited a slightly higher performance score than the HBB. Findings: The CFB exhibited good performance in terms of the dose on OARs and at the matching fields. This method offers a comparable level of performance to the HBB. Thus, the CFB offers an alternative method of significant interest in PMRT.