Hard Wedge Research Articles

In situ analysis of flow characteristic and deformation field of metal surface in sliding asperity contact

This work uses a model in situ configuration to explore the surface flow characteristics of a soft metal surface sliding against a hard wedge, representative of surface asperity. Digital image analysis shows that a sharp wedge triggers the non-laminar flow of materials which moves the strain rate field closure to the surface, causes surface folding, and generates cracks-likes features on the slid surface. Whereas, a blunt wedge with a large tip radius promotes laminar flow and suppresses the cracks. The transition of flow from laminar to non-laminar mode is discussed in terms of the underlying deformation characteristic of sliding wedges.

Review of Person, Thing, Robot by David Gunkel

David Gunkel has been questioning the traditional assumptions about cyberspace, machines, and artificial intelligence models for over a decade now. As a moral philosopher and communications expert, Gunkel, rightly, challenges the traditional Western ontology that has been intertwined with modern AI and robotics. In 2012, Gunkel published the first two works (The Machine Question, and 2018 Robot Rights), both of which called into question the current moral and ethical frameworks for thinking about machines. Person, Thing, Robot is the third installment to this trilogy of works. It is a work of ontology but also of deconstruction, for it takes the question of the ontology of humans and machines further by asking why objects do not fit neatly into the order of things. Gunkel also seeks to drive a hard wedge between the binaries of humans and machines that have long plagued the thinking around technology like AI and robots. How does Gunkel approach this endeavor?

Hybrid volumetric modulated arc therapy for hypofractionated radiotherapy of breast cancer: a\xa0treatment planning study

PurposeThis study aims to evaluate the best possible practice using hybrid volumetric modulated arc therapy (H-VMAT) for hypofractionated radiation therapy of breast cancer. Different combinations of H‑VMAT—a combination of three-dimensional radiotherapy (3D-CRT) and VMAT—were analyzed regarding planning target volume (PTV), dose coverage, and exposure to organs at risk (OAR).MethodsPlanning computed tomography scans were acquired in deep-inspiration breath-hold. A total of 520 treatment plans were calculated and evaluated for 40 patients, comprising six different H‑VMAT plans and a 3D-CRT plan as reference. H‑VMAT plans consisted of two treatment plans including 3D-CRT and VMAT. During H‑VMAT planning, the use of hard wedge filters (HWF) and beam energies were varied. The reference plans were planned with mixed beam energies and the inclusion/omission of HWF.ResultsCompared to the reference treatment plans, all H‑VMAT plans showed consistently better PTV dose coverage, conformity, and homogeneity. Additionally, OAR protection was significantly improved with several H‑VMAT combinations (p < 0.05). The comparison of different H‑VMAT combinations showed that inclusion of HWF in the base plan had a negative impact on PTV dose coverage, conformity, and OAR exposure. It also increased the planned monitor units and beam-on time. Advantages of using lower beam energies (6-MV photons) in both the base plan and in the VMAT supplementary dose were observed.ConclusionThe H‑VMAT technique is an effective possibility for generating homogenous and conformal dose distributions. With the right choice of H‑VMAT combination, superior OAR protection is achieved compared to 3D-CRT.

종류별 기능성 인솔 착용에 따른 하지근육의 근활성도 분석

The purpose of this study was to compare the difference in muscle activity of the lower extremity muscles according to the type of functional insole during normal walking. A total of fourteen male college students were recruited for this study. They were asked to walk with a general insole, a type A insole and a type B insole at a walking speed of 108 steps/min. To measure muscle activity of the lower extremities, EMG electrodes were attached to 7 muscles of the left lower extremity (gluteus medius, gluteus maximus, biceps femoris, gastrocnemius lateralis, adductor, rectus femoris, tibialis anterior). A one-way ANOVA was performed to compare the muscle activity (% RVC) of the lower extremity muscles according to the type of functional insole. The results showed that there were significant differences in biceps femoris (F=20.839, p=.000) and adductor (F=5.448, p=.008) among insole types. From the findings of this study, the following conclusions were derived: First, type A insole (with a mechanism to prevent arch deformation of the foot) was statistically significantly lower in biceps femoris activity than general and type B insoles due to the impact relaxation function of the material attached to the heel. Second, type B insole (supported by a hard wedge in the medial arch) was statistically significantly lower in adductor activity than type A insole, and thus can be effective in preventing the inversion or eversion of the foot.

Sinuous flow and folding in metals: Implications for delamination wear and surface phenomena in sliding and cutting

We demonstrate key features of a recently uncovered mode of plastic flow – sinuous flow – with vortex-like components on the mesoscale. Based on high-resolution, in situ imaging of a hard wedge (asperity) sliding against a metal surface, we contrast this flow with the more well-known smooth homogeneous (laminar) flow in wear and large strain deformation processes. Sinuous flow is characterized by folding, and arises in both pure sliding and cutting of metals with large strain hardening capacity. The folds mediating the flow can transform into wear particles and surface defects by delamination via fold-splitting. Examples of this occurrence have been captured in situ, by high speed imaging of the sliding contact. This provides a direct mechanism for delamination wear, in just a few passes of sliding. Material heterogeneity plays an important role in the folding, as revealed by finite element simulation and experiment. This combined experiment-simulation approach reveals a number of ways in which folding can be triggered, suggesting an important role for sinuous flow in delamination wear. A close relationship between sinuous flow and mechanochemical Rehbinder effects in machining of metals is also highlighted. Technological implications of sinuous flow for sliding wear and manufacturing processes are briefly discussed.

УСТОЙЧИВОСТЬ ГРУНТОВОЙ ПЛОТИНЫ С ВЕРТИКАЛЬНОЙ ДИАФРАГМОЙ

Earth dam with impervious element in the form of asphaltic concrete core is currently the most promising type of earth dams (due to simple construction technology and universal service properties of asphaltic concrete) and is widely used in the world. However, experience in the construction and operation of high dams (above 160 m) is not available, and their work is scarcely explored. In this regard, the paper discusses the results of computational prediction of the stress-strain state and stability of a high earth dam (256 m high) with the core. The authors considered asphaltic concrete containing 7 % of bitumen as the material of the core. Gravel was considered as the material of resistant prisms. Design characteristics of the rolled asphaltic concrete and gravel were obtained from the processing of the results of triaxial tests. The calculations were performed using finite element method in elastoplastic formulation and basing on the phased construction of the dam and reservoir filling. The research shows, that the work of embankment dam with vertical core during filling of the reservoir is characterized by horizontal displacement of the lower resistant prism in the tailrace and the formation of a hard wedge prism descending along the core in the upper resistant prism. The key issue of the safety assessment is to determine the safety factor of the overall stability of the dam, for calculation of which the destruction of the earth dam is necessary, which can be done by reducing the strength properties of the dam materials. As a results of the calculations, the destruction of the dam occurs with a decrease in the strength characteristics of the materials of the dam by 2.5 times. The dam stability depends on the stability of the lower resistant prism. The destruction of its slope occurs on the classical circular-cylindrical surface. The presence of a potential collapse surface in the upper resistant prism (on the edges of the descending wedge) does not affect the overall stability of the dam.

Quantitative In Situ Analysis of Deformation in Sliding Metals: Effect of Initial Strain State

Using in situ, high-speed imaging of a hard wedge sliding against pure aluminum, and image analysis by particle image velocimetry, the deformation field in sliding is mapped at high resolution. This model system is representative of asperity contacts on engineered surfaces and die-workpiece contacts in deformation and machining processes. It is shown that large, uniform plastic strains of 1-5 can be imposed at the Al surface, up to depths of 500 mu m, under suitable sliding conditions. The spatial strain and strain rate distributions are significantly influenced by the initial deformation state of the Al, e.g., extent of work hardening, and sliding incidence angle. Uniform straining occurs only under conditions of steady laminar flow in the metal. Large pre-strains and higher sliding angles promote breakdown in laminar flow due to surface fold formation or flow localization in the form of shear bands, thus imposing limits on uniform straining by sliding. Avoidance of unsteady sliding conditions, and selection of parameters like sliding angle, thus provides a way to control the deformation field. Key characteristics of the sliding deformation such as strain and strain rate, laminar flow, folding and prow formation are well predicted by finite element simulation. The deformation field provides a quantitative basis for interpreting wear particle formation. Implications for engineering functionally graded surfaces, sliding wear and ductile failure in metals are discussed.

Cardiopulmonary Resuscitation in the Pregnant Patient

Summary The importance of minimising aortocaval compression during cardiopulmonary resuscitation in late pregnancy is widely accepted. Current European guidelines suggest employing manual displacement of the uterus with left lateral tilt to achieve this. Several methods for producing lateral tilt have been described; however, the optimum method is unknown. By performing simulated cardiopulmonary resuscitation on a manikin, we compared four of these methods: a folded labour ward pillow; a pre-formed foam wedge; a custom-made hard wooden wedge; and the ‘human wedge’. Primary outcome measures were maintenance of adequate tilt, stability and effectiveness of chest compressions (rate, depth and adequate release). Overall, the foam and wooden wedges were significantly more stable and reliable at maintaining tilt than the pillow (p < 0.0001); the wooden wedge was more stable and effective than the foam wedge (p < 0.0001). Chest compressions were least effective with the human wedge (p = 0.02). Effectiveness of chest compressions with lateral tilt was comparable to that reported previously in supine manikin studies. We recommend the use of dedicated foam or hard wedges rather than pillows or the human wedge for producing lateral tilt during cardiopulmonary resuscitation.

Surface flow in severe plastic deformation of metals by sliding

An in situ study of flow in severe plastic deformation (SPD) of surfaces by sliding is described. The model system – a hard wedge sliding against a metal surface – is representative of surface conditioning processes typical of manufacturing, and sliding wear. By combining high speed imaging and image analysis, important characteristics of unconstrained plastic flow inherent to this system are highlighted. These characteristics include development of large plastic strains on the surface and in the subsurface by laminar type flow, unusual fluid-like flow with vortex formation and surface folding, and defect and particle generation. Preferred conditions, as well as undesirable regimes, for surface SPD are demarcated. Implications for surface conditioning in manufacturing, modeling of surface deformation and wear are discussed.

An institutional experience of quality assurance of a treatment planning system on photon beam

AimThe purpose of the present study is to show the application of the IAEA TRS-430 QA procedures of Eclipse™v7.5 TPS for photon energies. In addition, the trends of the deviations found in the conducted tests were determined. BackgroundIn the past, the lack of complete TPS QA procedures led to some serious accidents. So, QA in the radiotherapy treatment planning process is essential for determination of accuracy in the radiotherapy process and avoidance of treatment errors. Materials and methodsThe calculations of TPS and measurements of irradiations of the treatment device were compared in the study. As a result, the local dose deviation values (δ1: central beam axis, δ2: penumbra and build up region, δ3: inside field, δ4: outside beam edges, δ50–90: beam fringe, RW50: radiological width) and their confidence limit values (including systematic and random errors) were obtained. ResultsThe confidence limit values of δ4 were detected to increase with expanding field size. The values of δ1 and δ3 of hard wedge were larger than open fields. The values of δ2 and δ50–90 of the inhomogeneity effect test were larger, especially than other tests of this study. The average deviation was showed to increase with the rise of the wedge angle. The values of δ3 and δ4 of lung irradiation were outside tolerance. ConclusionsThe QA of TPS was done and it was found that there were no reservations in its use in patient treatment. The trend of the deviations is shown.

SU‐E‐J‐145: Dosimetric Impact of Patients Set‐Up Effect in Radiation Therapy Planning System for Breast Cancer Patients with Conventional Wedge and Field‐In‐Field Techniques

Purpose: To evaluate the dosimetric effects of patients setup errors and breathing movement on whole breast irradiation with conventional hard wedge (HW) and field‐in‐field (FIF) techniques. Methods: A total of 10 patients who received whole breast irradiation were chosen for this study. We performed radiation treatment planning for whole breast irradiation with two techniques; conventional hard wedge (HW) and field‐in‐field (FIF). On the subject of each patients, ‐ original plan‐was created using the general clinical planning technique and then we generated ‐ isocenter shift plan‐and ‐ gantry angle shift plan‐to evaluate dose variation according to change of isocenter and gantry angle. In our study, the isocenter was shifted by 0.6 cm for the right‐left, 0.5 cm for superior‐inferior, and 1.4 cm for anterior‐posterior direction refer to Kinoshita et al. study. Assuming that breast shape changes subtly, the gantry angle was shifted from 1° to 5° each tangential fields. To analysis the plan quality this study calculated a dose‐volume histogram (DVH) and the dose indices that are mean dose of CTV, CTV D95, CTV V95, lung V20, heart V40 and PTV dose improvement (PDI) index. Results: When isocenter of lung and heart shifted in the right‐left and superior‐inferior direction, ‐ isocenter shift plan‐showed no significant variation from ‐ original plan‐for most of the indices. However, a significant difference was found in V95 of CTV with isocenter shift in anterior‐posterior direction by assuming the patient shifted in the posterior direction. Shifts in gantry angle slightly affected lung and heart, and smaller changes were seen in PTV. Conclusions: This study evaluated the dosimetric effects of gantry angle and isocenter shift for simulating patients setup errors and breathing motion. The effects of patient and breast changes during treatment could have influence on dose distribution of OARs as well as that of PTV.

Heuristic Physical Theory of Diffraction for Impedance Polygon

A heuristic physical theory of diffraction (PTD) for an acoustic impedance wedge is proposed. This method is based on Ufimtsev's three-dimensional PTD, which is derived for an acoustic soft or hard wedge. We modify the original PTD according to the process of physical optics (or the Kirchhoff approximation) to obtain a 3D heuristic diffraction model for an impedance wedge. In principle, our result is equivalent to Luebbers' model presented in electromagnetism. Moreover, our approach provides a useful insight into the theoretical basis of the existing heuristic diffraction methods. The derived heuristic PTD is applied to an arbitrary impedance polygon, and a simple PTD formula is derived as a supplement to the physical optics formula.

SU‐E‐T‐127: Two Dosimetric Methods of Measuring Linac Beam Spot Position

Purpose: Two dosimetric methods of measuring the electron beam spot position of photon beams w.r.t. the Collimator Axis Of Rotation (CAOR) are described. Methods: Method 1 (SNG test) uses a cylindrical ion chamber (IC) (A1SL) in a phantom mounted on a jig co‐rotational with the collimator making the relationship among the chamber, phantom, jaws and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the phantom adjusted so the IC signal is 65% of the open field value. cGy/mu is measured every 30 degrees of collimator rotation. The phantom is then translated normal to the IC axis until the signal is 35%. The shift is recorded to calculate sensitivity (%dose/mm). For a radially symmetric spot centred on CAOR, the IC signal is angularly constant. Deviation from constant indicates a displacement from the CAOR and a shape distortion. The displacement and spot shape are calculated using Fourier analysis and penumbra shape (sensitivity). The 2nd method uses a hard wedge instead of the jaw and sensitivity is obtained from wedge profiles. Test measurements were performed on an Elekta 6 MV: the In Plane beam spot position was measured before and after it was moved by changing bending magnet current (Bending Fine). Results: Independent beam spot measurement (Flexmap Image Registration) showed the initial beam spot, projected back to source, 0.29 mm from CAOR, moving to 0.91 mm (delta=0.62 mm) with steering. The SNG test reported the beam spot moving from 0.13mm to 0.92 mm from CAOR (delta=0.79 mm). The hard wedge test gave an initial position of 0.09 mm off axis and a final position of 0.79 mm (delta=0.7 mm) Conclusions: The methods described provide a quantitative measure of beam spot position, not requiring the user to independently define the CAOR.Jason Smale is an Employee of Elekta Canada

Wedging of an edge crack in the elastic wedge

We study the problem of wedging of an elastic wedge realized along the edge crack with the help of a hard wedge. The analytic solution of the problem is obtained by the Wiener-Hopf method. We determine the stress intensity factors, the distributions of stresses on the continuation of the crack and in the contact zone, and the circular displacements of the crack lips.

Performance Evaluation of Field-In-Field Technique for Tangential Breast Irradiation

Conventional hard or dynamic wedge systems are commonly applied to reduce the dose inhomogeneity associated with whole breast irradiation. We evaluated the dosimetric benefits of the field-in-field (FIF) technique by comparing it with the electronic compensator (EC), Varian enhanced dynamic wedge (EW) and conventional hard wedge (HW) techniques. Data were obtained from 12 patients who had undergone breast-conserving surgery (six left-sided and six right-sided). For these patients, the average breast planning target volume (PTV) was 447.4 cm(3) (range, 211.6-711.8 cm(3)). For the experiments, a 6 MV photon beam from a Varian 21 EX was used, the HW and EW angles were applied from 15 to 45 degrees, while 40-50% isodose values were chosen to achieve the best dose distribution for electronic compensation. In applying the FIF technique, we used two or three subfields for each portal. To evaluate the performance for each planning technique, we analysed a dose-volume histogram (DVH) for the PTV and organs-at-risk (OARs). To evaluate the effects of these techniques on dose inhomogeneity, we defined the PTV Dose Improvement (PDI) index, which was derived from a PTV volume between 97-103% of the differential DVHs. In addition, we compared the average monitor units (MUs) for each technique. The average PDI index with FIF is 76.4%, while the PDI indices for other treatments were 65.8, 41.8 and 50.9% for EC, EW and HW, respectively. This study demonstrated an improved performance using the FIF technique compared with the conventional HW/EW system, as well as a new modality for EC. We demonstrated that FIF is a very useful technique for improving PTV conformity, while protecting the OARs from breast tangential irradiation.

SU-FF-T-12: A Critical Review of the Performance of Varian's New Anisotropic Analytical Algorithm (AAA) Utilized in Photon Treatment Planning

Purpose: To critically review the performance of the Anisotropic Analytical Algorithm with respect to accuracy across a complete range of 3D and IMRT treatment fields and its ability to account for tissue heterogeneities, hard and dynamic wedges, multileaf collimated beams and dynamic leaf motions. Method and Materials: AAA generated monitor units are compared with predicted monitor units generated by measurements at central axis in a water phantom for open fields, hard and dynamic wedges and multileaf collimated fields. AAA predicted doses are compared against measured doses in a anthropomorphic chest phantom in a complex arrangement of beams for both 6 and 18 MV photons, multileaf collimated beams and dynamic wedges. AAA predicted isodose curves are compared by digital subtraction against film recorded isodose curves. Results: For 6 and 18 MV photons open field beams had an average error of 0.01 and 0.00% and a maximum error of 1.17 and 1.24%; hard wedged fields had an average error of 0.12 and 0.53% and a maximum error of 1.16 and 2.32%; dynamic wedges had an average error of 1.28 and 1.87 and a maximum error of 3.3 and 4.8% respectively. These measurements had a measurement error of ±1%. In the chest phantom measurements the dose was evaluated for 1) Isocenter dose, 2) Off‐axis dose, and 3) Out‐of‐field dose. The results showed for 6 and 18 MV the average error was 1) 2.3%, 0.4%, 2) 0.7%, 4.4% and 3) 0.2%, 0.3% respectively. The digital subtraction analysis showed similar results and is displayed and analyzed. Conclusion: The AAA algorithm is a robust and accurate calculation engine. It shows consistent accuracy throughout the useful range of field sizes and depths. It demonstrates an improved accuracy with hard wedge beam hardening and tissue heterogeneities and successfully manages electron contamination above 5 cm in depth.

Modal Analysis of the GTD Diffraction Coefficients for the Half-Plane’s Edge

The GTD diffraction coefficients for the half-plane’s edge are obtained by a new semi-analytic approach: From the modal expansion of the Green’s function of an acoustically soft or hard wedge the total field due an incident plane wave is derived by locating a line source at infinity and by transforming the incident line-source field to an incident plane-wave field. By means of the second Green’s theorem and by using the bilinear form of the free-space Green’s function, the scattered far field is obtained from the exact field values on the wedge’s flanks. The isolated edge-diffracted part can be identified as the difference between the far field scattered by a half plane and one half of the far field scattered by the entire plane. The obtained alternating and —in the classical sense— non-converging series are numerically evaluated by means of a linear (consistent) summation technique, and the comparison to Keller’s result shows excellent agreement. The main advantage of this new method is that it can be applied to a certain class of more difficult problems (circular and elliptic cone, plane angular sector, etc.).

Diffraction of sound from a dipole source near to a barrier or an impedance discontinuity.

Pierce's formulation for the diffraction of spherical waves by a hard wedge has been extended to the case of the sound field due to a dipole source. The same approach is also used to extend a semiempirical model for sound propagation above an impedance discontinuity due to a dipole source. The resulting formulas have been validated by comparing their numerical solutions with that computed by summing the sound fields due to two closely spaced monopole sources of equal magnitude but opposite in phase. These new formulations are then used to develop a simple model for calculating the dipole sound field diffracted by a barrier above an impedance ground. Applications of these models relate to transportation noise prediction, particularly railway noise abatement, for which dipole sources are commonly used. The numerical predictions have been found to compare reasonably well with indoor measurements using piezoceramic transducers as dipole sources.

Noise attenuation by a hard wedge-shaped barrier

This paper is concerned with the problem of sound screening by a wedge-like barrier. The sound source is assumed to be point like, and the receiver is located in the shadow of the source sound field, so that according to geometrical optics only the field diffracted by the edge of the barrier is considered. First, for the hard wedge in space, three models are used for calculating the amplitude of the edge-diffracted field. These are the uniform theory of diffraction (UTD), the Hadden–Pierce model, both in the frequency domain, and the Biot–Tolstoy theory of diffraction which is a time domain formulation. It is first shown that even at relatively low frequencies, the frequency domain models perform quite satisfactorily as compared to the exact time domain theory. Hence, and due to its relative simplicity the UTD is proposed as an accurate calculation scheme for solving problems with edge diffraction by hard wedges. It is also proved from theoretical calculations that the amplitude of the edge-diffracted field increases for an increasing angle of the wedge, and consequently the hard half-plane gives the lowest field amplitude in the shadow zone. Some applications are then considered for evaluating the performance of a barrier on a flat ground, either completely hard or with mixed homogeneous boundary conditions. An improvement of the scheme for calculating the sound field in the all-hard case is achieved through considering the multiple diffraction, in this case only to the second order, between the top of the wedge barrier and its base. The results show that for usually occurring situations, increasing the angle of the hard wedge barrier affects negatively its efficiency through diminishing its insertion loss. These conclusions are also supported by the results of some experimental measurements conducted at a scale-model level.

SOUND SCATTERING BY A HARD HALF-PLANE: EXPERIMENTAL EVIDENCE OF THE EDGE-DIFFRACTED WAVE

In this short note, some experimental results are presented on the diffraction of a spherical way by a hard half-plane. This study was conducted with the aim to give evidence to the existence of the edge-diffracted wave. The sound source used in this experimental study is a condenser microphone operating in a reverse way. The wave emitted by a sound source propagates in space and hits a thin aluminium sheet with a straight edge, considered as an idealization of the hard half-plane. The resulting impulse response includes among others a wave diffracted by the edge of the half-plane, which is compared to its theoretical prediction. This latter is calculated from the exact Biot and Tolstoy solution to the problem of diffraction of a spherical wave by a hard wedge. Relatively satisfactory agreement is found between theory and experiment.