Actual Edge Research Articles

A method for geometrical verification of dynamic intensity modulated radiotherapy using a scanning electronic portal imaging device.

In order to guarantee the safe delivery of dynamic intensity modulated radiotherapy (IMRT), verification of the leaf trajectories during the treatment is necessary. Our aim in this study is to develop a method for on-line verification of leaf trajectories using an electronic portal imaging device with scanning read-out, independent of the multileaf collimator. Examples of such scanning imagers are electronic portal imaging devices (EPIDs) based on liquid-filled ionization chambers and those based on amorphous silicon. Portal images were acquired continuously with a liquid-filled ionization chamber EPID during the delivery, together with the signal of treatment progress that is generated by the accelerator. For each portal image, the prescribed leaf and diaphragm positions were computed from the dynamic prescription and the progress information. Motion distortion effects of the leaves are corrected based on the treatment progress that is recorded for each image row. The aperture formed by the prescribed leaves and diaphragms is used as the reference field edge, while the actual field edge is found using a maximum-gradient edge detector. The errors in leaf and diaphragm position are found from the deviations between the reference field edge and the detected field edge. Earlier measurements of the dynamic EPID response show that the accuracy of the detected field edge is better than 1 mm. To ensure that the verification is independent of inaccuracies in the acquired progress signal, the signal was checked with diode measurements beforehand. The method was tested on three different dynamic prescriptions. Using the described method, we correctly reproduced the distorted field edges. Verifying a single portal image took 0.1 s on an 866 MHz personal computer. Two flaws in the control system of our experimental dynamic multileaf collimator were correctly revealed with our method. First, the errors in leaf position increase with leaf speed, indicating a delay of approximately 0.8 s in the control system. Second, the accuracy of the leaves and diaphragms depends on the direction of motion. In conclusion, the described verification method is suitable for detailed verification of leaf trajectories during dynamic IMRT.

Nucleation and overgrowth of PE on PTFE/iPP interfaces

Using an experimental setup with a three-phase intersecting boundary of PTFE/PE/iPP, the nucleation power of PTFE compared to iPP on the PE was studied by TEM. It was found that the nucleation of the PE on the PTFE interface started at a higher temperature than epitaxial nucleation of the PE onto the iPP interface. During cooling of the melt, the growth direction of the PE crystalline lamellae changes in a continuous manner from the transcrystallization direction of the PTFE/PE interface into the heteroepitaxial “crosshatched” orientation of the iPP/PE interface. A (still highly speculative) self-assembly of the PE macromolecules at the respective interface just in front of the actual crystallization edge is used to explain this observed phenomenon. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 80–83, 2000

Scalable parallel implementations of list ranking on fine-grained machines

We present analytical and experimental results for fine-grained list ranking algorithms. We compare the scalability of two representative algorithms on random lists, then address the question of how the locality properties of image edge lists can be used to improve the performance of this highly data-dependent operation. Starting with Wyllie's algorithm and Anderson and Miller's randomized algorithm as bases, we use the spatial locality of edge links to derive scalable algorithms designed to exploit the characteristics of image edges. Tested on actual and synthetic edge data, this approach achieves significant speedup on the MasPar MP-1 and MP-2, compared to the standard list ranking algorithms. The modified algorithms exhibit good scalability and are robust across a wide variety of image types. We also show that load balancing on fine grained machines performs well only for large problem to machine size ratios.

The methods of detection and the analysis of welded and brazed joint defects emerging during ITER components manufacturing

The nondestructive testing (NDT) methods to test materials and welds in the bearing structures of a superconducting magnet system, vacuum vessel and divertor are described. The experimental results are presented on estimating the efficiency of different NDT methods to identify the type and to assess the size of defects in mock-ups and components manufactured by applying the technologies to be used for the commercial production of the real ITER systems. The results are given on detecting and assessing actual defect-like cracks, sagging and edge displacement in the titanium cylindrical jacket during the commercial manufacture of the experimental conductor samples. The analysis of the results allows the conclusion to be made on a comparative efficiency of different NDT methods for the detection of defects arising during ITER component manufacture.

An incremental theory of diffraction: scalar formulation

A formulation is introduced that provides a self-consistent, high-frequency description of a wide class of scattering phenomena within a unified framework. This method is based on the appropriate use of locally tangent canonical problems, with a cylindrical uniform configuration and arbitrary cross section. A generalized localization process is applied to define incremental diffracted field contributions, which are adiabatically distributed along the actual edge discontinuities or shadow boundary lines. Then, the total field is represented as the sum of a generalized geometrical optics field plus incremental diffracted field contributions. This representation of the field is uniformly valid at any incidence and observation aspects, including caustics and shadow boundaries of the corresponding ray field description. This method naturally includes the uniform GTD ray field representation of the scattering phenomenon, when it is applicable. For the sake of convenience in the explanation, the formulation for scalar problems is discussed in this paper. The formulation for vector, electromagnetic problems is given in the subsequent paper on electromagnetic formulation. It is suggested that this method may provide a quite general, self-consistent procedure for predicting the field scattered in the near as well as in the extreme far zone of an arbitrarily shaped, opaque object. >

Neural network model for generating subjective contours

AbstractThe human visual system has the ability to recognize a virtual line even for a discrete object such as a dot pattern. Even if there is no difference in color or brightness, a clear subjective contour can still be perceived. This phenomenon can be formulated as an interpolation problem.This paper proposes a hierarchical visual information‐processing model based on physiological data. The model then is applied to the problem of interpolation, e.g., the perception of a virtual line and a subjective contour. To form the subjective contour, the actual outline of the visual object, the points comprising the subjective contour and the points that move to form a subjective contour must be determined. This is achieved by parallel processing in the proposed model which is composed of complex cells and hyper‐complex cells.The complex cells receive the outputs of two kinds of simple cells (S and L), and executes contour detection and interpolation of a dot pattern by global processing. The hypercomplex cell detects the end point and the point of large curvature through which the subjective contour is supposed to pass. All these processes are executed by parallel processing.When the results of processing are ready, the points comprising the subjective contour are determined by weighting. The model in this study is constructed to detect the subjective contour as well as the actual edge by assembling the information from these hierarchical processing.

Spatial variations in the charge density of argon discharges in the Gaseous Electronics Conference reference reactor

The spatially dependent ion and electron concentrations of argon discharges in the gaseous electronics conference reference reactor reach a saddle point maximum in the center of the glow. The concentrations were measured using a Langmuir probe. The charge density decreases in the axial direction from the glow center to the electrode sheath edges as expected. In contrast, the charge density increases in the radial direction from the glow center to the radial electrode edge. The maximum occurs approximately 1 cm inside of the actual electrode edge. The most plausible explanation for this increase is enhanced ionization at the electrode edges due to field enhancement there. The electric field is enhanced by the close proximity of the ground shield and driven electrode at the radial edge of the electrode. We estimate that the ionization rate in the plasma near the electrode edge must be almost double of that in the glow center.

Delayed relaxation in thin-film heads

The delayed relaxation after writing with a Permalloy thin-film head has been studied experimentally. The phenomenon of delayed relaxation is shown to be caused predominantly by stress-induced relaxation of the flux closure domains along the edges of the thin-film-head yoke. It is necessary for this effect that the composition of the Permalloy yields nonzero magnetostriction. The fairly rapid temperature change directly after write will then trigger irreversible wall displacements which show up as transient noise pulses in the head output. Depending on the actual edge domain relaxation, these transients can have a positive or a negative polarity, or can be bipolarity transients. This thermomechanically triggered irreversible wall-motion process can fairly accurately be modeled as a Poisson process. The model predicts the arrival time distribution, the probability of occurrence for different write currents, and threshold settings reasonably well. This 'noise-after-write' effect can be made smaller by striving for zero magnetostriction and a lower write power dissipation, and to some extent by increasing the thermal conductivity to the slider.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Absolute kVp calibration using characteristic x-ray yields.

A spectrometer with a high-resolution room-temperature silicon detector was used to obtain spectra including characteristic x-ray peaks produced after fluoroscopic beams were incident on W, Pb, and Th absorbers. Characteristic x-ray yield points were obtained from spectra taken at several generator kVp settings which produced x rays with energy above the K-shell absorption edge for each element. A line drawn through the yield points when projected to zero yield served to locate the console setting corresponding to the actual K-absorption edge energy for each absorber. The technique is useful for precision measurement of generator kVp and absolute calibration of indirect kVp measuring devices under operational conditions.

Two-dimensional simulation of MODFET and GaAs gate heterojunction FET's

Previous simulation studies on heterojunction devices have been limited to idealized device structures (mostly 1-D) which neglect important parasitic effects. In order to realistically simulate heterojunction devices, a general two-dimensional device simulator has been developed which includes for the first time features essential to designing and modeling realistic devices, for example, multiple heterolayers, a modified mobility model for the 2-D electron gas, Fermi level pinning at the surfaces, and deep traps in the substrate. Two specific types of high electron mobility heterojunction devices have been studied and compared. The first type is the recessed-gate MODFET and the second type is the GaAs gate heterojunction FET. At 77 K, simulation results showed that high transconductances (450-500 mS/mm) can be obtained for both types of structures with similar geometries. For GaAs gate FET's, the device operation is found to be sensitive to the surface defect density in the ungated gap of the self-aligned T-gate structure, while for a similar MODFET structure with an analogous gap between the actual recessed edge and the gate edge, the dependency on the surface defect density is relatively weak because the AlGaAs layer is rather heavily doped. The causes for the transconductance degradation of MODFET's have been identified as either the neutralization of the ionized impurities in the AlGaAs layer or the saturated resistor under the ungated gap in the recessed region.

Method of Determining the Actual Form of the Tool Edge from Chips

A method has been proposed by which a variety of actual cutting edge forms in cutting can be estimated from the information obtained with the observation of longitudinal section of chips only, and graphs illustrated by this method are presented. The formulas by which the actual rake angle in cutting can be calculated with the lattice pattern or the fibrous structure in the work deformed are induced. By applying these methods, the shape of built-up edge, the actual edge of restricted tool, in cutting, and so forth have been determined. And then, experiments have been carried out to substantiate these methods. The results coincide with the theory.

Deburring precision miniature parts

Precision parts demand care not only in the generation of dimensions and surfaces, but also in subsequent finishing operations. Deburring and edge finishing are two areas often given little consideration by those designing or machining such parts. Due to the lack of data and difficulty involved, it is common for deburring of precision parts to require up to 30% of the total part costs, and even more when the parts are small. Some basic design and fabrication guidelines are available as a result of recent research which provide a scientific method for specifying edge quality and choosing appropriate deburring processes. The basic constraint to deburring and edge finishing is minimising burr size and defining actual edge quality requirements

How accurate is the visual assessment of basal carcinoma margins?

SUMMARY This study evaluated the accuracy of visual determination of tumour margins in basal cell carcinomas. Using a 2.5 × binocular magnifier, the apparent tumour margin was marked pre-operatively by light electrodesiccation. Following excision, the electrodesiccation mark was compared to the actual tumour edge by microscopy of step level sections. It was possible to delineate the tumour margins with an accuracy of 1 mm in 94% of a selected series of 101 basal cell carcinomas. These findings support the view that a 2 mm margin of normal tissue is adequate in the surgical treatment of most basal cell carcinomas.

Gastric ulcer: clinical observations on cure rate, relapse rate, and possible malignant change

1) Cure rate Cure rate of gastric ulcers of the in-patient group are distinctly better than the out-patient group. And cure rates are related to the diameter and to the depth of the crater. 2) Relapse rate The relapse rate is highest in the group subjected to the longest periods of follow-up observation. More than 50% of relapsed gastric ulcer group were relapsed within one year and nearly 75% within two years. Relapses occured most commonly in the third, forth and fifth decades, less commonly in the older and younger age groups. And there is no statistical significance in the relationship between the sex, size, depth or location of the initial ulcer and relapse rate. From histological studies of stomachs resected because of relapse, it was noted that the relapsed ulcers occured very close to or at the actual edge of the previous healed ulcer. Relapses occured more frequently in that group which healed their ulcers in a longer time period than the group in a shorter time period. It is to be noted that smoking, irregular mealtime, physical and mental overwork, sleeplessness and general dietary habits were statiscally significant as tiological factors in gastric ulcer relapse. And more than one out of the above six important etiological factors were present coincidentally in a larger number of the relapsed ulcer cases. Relased ulcer take longer to heal than required for the healing of the initial ulcer. 3) Malignant changes From our follow-up study on 991 cases of healed gastric ulcers, only 4 cases may have changed from benignity to malignancy. We believe that it is safe to say that the rate of malignant change is extremely low in a ten year follow-up study.

The blade edge microscope of the Netherlands Ship Model Basin

For a reliable testing of propellers on cavitation the shape of the first few milimeters of the leading edge of the screw blade, corresponding with 1 to 2% of the chord, is very important. If the model propeller leaves the workshop, its leading edges neither have the right shape nor are they identi cal. These differences can usually not be seen by the unaided eye but in the tunnel they result in drastic differences in the cavitation inception of the blade. In order to help the workshop to produce model propellers which are dimensionally more accurate, a microscope mounted on a special rig is put into use. With the aid of this new apparatus the actual blade edge shape can be optically compared with the prescribed one. If not correct the blade edge can be filed down. Tunnel tests with a standard Wageningen B-series propeller illustrate the importance of leading edge shape on the inception and extent of cavitation.

The Initial Buckling of Slightly Curved Panels Under Combined Longitudinal and Circumferential Direct Stresses

SummaryThe initial buckling stresses of rectangular panels under applied axial loads are in general increased both by circumferential tensile stresses and by the curvature of the panel. The present Note gives theory to estimate these stresses for panels forming part of an unstiffened cylindrical shell. All edges are free to rotate. This condition is often closer to the actual rotational edge restraint of curved panels in conventional stressed-skin construction than the clamped condition, especially in the case of lightly-reinforced shells. The axial generators in the mid-plane of the panels are held straight at the longitudinal edges. All other axial generators are also assumed to remain straight before buckling (no “mattress effect”). The middle surface is restrained at the curved edges of the panel against radial deformation during and after buckling.Design curves are presented for several values of the parameter (ab/Rt), followed by a typical example.

Intrinsic Optical Absorption in Tellurium

Measurements of intrinsic optical absorption have been made at 100 and 300\ifmmode^\circ\else\textdegree\fi{}K by transmission techniques, covering a range of absorption coefficient from 0.01 ${\mathrm{cm}}^{\ensuremath{-}1}$ to 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ for radiation polarized E\ensuremath{\parallel}C, and to 5000 ${\mathrm{cm}}^{\ensuremath{-}1}$ for E \ensuremath{\perp} C. These results suggest that the edge is set by vertical transitions, the transition being allowed for the polarization E \ensuremath{\perp} C but forbidden for E\ensuremath{\parallel}C. Absorption above the intrinsic threshold is apparently influenced by electron-hole interaction, as postulated by Elliott. In the actual edge region, absorption falls off exponentially with decreasing photon energy, the steepness at 300\ifmmode^\circ\else\textdegree\fi{}K being 197 e${\mathrm{V}}^{\ensuremath{-}1}$ for E\ensuremath{\parallel}C and 267 e${\mathrm{V}}^{\ensuremath{-}1}$ for E \ensuremath{\perp} C. The steepness for each polarization increases by only 14% on cooling to 100\ifmmode^\circ\else\textdegree\fi{}K.

The Bright Clouds and the Aurora

ON the morning of the 11th inst. I had an opportunity of watching the curious cirrus-like clouds as daylight came on. The display was striking, though not such a bright one as on several former occasions. It first appeared about 2.30 a.m., when there were very faint indications of the clouds; it was some minutes before I noticed that they were the same brilliant kind as has appeared so often this summer. Their apparent upper border being irregular, it was uncertain whether they in any part reached the limit to which the sun could shine upon them, or whether the apparent border was altogether the actual edge of the cloud-sheet; however, it rose higher as the sun approached the horizon, but this might be owing to the circumstance that the motion of the clouds was, as usual, from an easterly direction. At 3.33½ a.m. they were visible as far as α Andromedae, though they were very faint west of γ. By 3.45½ a.m. they reached down to within 5° of α Aquilae, and were rather plain there, and by this time the sheet covered most of the sky, though none of it remained visible very low down in the east. It was no longer bright in any part. At 3.55½ they reached down to within 4° of α Aquilae, and were plainest about there, but growing fainter. I was still uncertain whether the sheet extended beyond the western apparent border, that being simply the limit of sunshine, or whether the sheet ended there; but probably the former was now the case. At 4 a.m. they were scarcely noticeable, and by 4.11 they had disappeared altogether. By this time a faint pink glow had appeared in the east.