Edge Slopes Research Articles

Direct Land Grading Design of Irrigation Plane Surfaces

Existing land grading design methods involve trial and error procedures to determine the plane that balances cut and fill volumes, considering the shrinkage of soil, to minimize earthwork. This paper presents simple formulas for direct land grading design that eliminates the need for trial and error procedures. The design formulas explicitly consider specifications which may include the two edge slopes of the plane, one edge slope and a control point, or two control points. The formulas are based on the assumption that the before and after‐grading volumes measured from a reference elevation are equal; the computed plane provides equal cut and fill volumes. Adjustment factors to account for the shrinkage of soil are then developed and can be applied to directly determine the position of the plane that satisfies the required cut/fill volume ratio. Application of the complete design procedure is illustrated by a numerical example.

A figure of merit for contrast study in two-dimensional structures

Image contrast and edge slope are frequently used to assess image quality. But in the case of two‐dimensional geometries, the definition of contrast is not appropriate, as the maximum and minimum values of intensities may be different at the center, corners, etc. Similarly, edge slope may be different in different planes. Recently, a figure of merit (FOM) has been proposed to evaluate the image quality of two‐dimensional structures by a single parameter. In this paper, both contrast and FOM have been calculated as a function of the parameters of the optical system. It has been shown that in the case of near micron geometries, the variation in the contrast and edge slopes is sometimes misleading, whereas the FOM gives more accurate information of the image fidelity.

On simulation of resist profiles in electron beam lithography

Resist profiles in electron beam exposed PMMA have been simulated before and after proximity exposure compensation (correction) for isolated and closely spaced line patterns. Edge slope of the resist profiles obtained in the two cases (before and after proximity exposure compensation) indicate the effectiveness of the compensation technique. Along with the edge slopes the line width variations are also determined.

Simulation of resist profiles in single and triple layer electron beam lithography

Resist profiles in PMMA are simulated for the case of single and triple layer electron beam lithography. Line width variations and edge slopes are compared in two cases. Improvements in line width variation and edge slopes have been shown to occur after proximity exposure correction. Further in the case of a triple layer by changing the transfer layer from low At No. silicon to high At No. tungsten, the required dose is less due to increased proximity exposure closer to the beam in tungsten. Resist profile simulation of closely spaced line patterns shows that a bridge between the patterns results which is eliminated after proximity exposure correction.

Computation of optical image profile for lithography and linewidth measurement

Optical microlithography for VLSI requires that the imaging process be well characterised and understood. Optical imaging is largely by projection such as in step-and-repeat cameras in mask making and projection aligners and direct steppers in wafer exposure systems. Image formation through a lens has been simulated in the literature in order to understand and predict the geometries that will be available on photoresist layers. The following assumptions are normally made regarding the exposure system: (a) the object is a mask containing a grating of a given period and (b) the opaque areas of the grating have zero transmittance and zero thickness. Such an assumption is valid for mask made of dark chrome for example. However, finite thickness and transmittance of the film can give rise to the differences in the computed image. A computer programme has been developed which computes the image profile taking into consideration the finite thickness of a film such as chrome or iron oxide. The illumination has been assumed to be partially coherent and the optics have been assumed to be diffraction limited. Intensity profiles for various linewidths less than 5 microns were calcualted. These were compared with intensity profiles obtained by SAMPLE which does not take into consideration finite transmittances of chrome or iron oxide layers. It has been found that both the linewidths and edge slopes of the image are quite different and the error can be as large as. 25 micron. The results of these computations are presented in this paper.

Statistical characterization of digital communication channels

Bit-error rate and eye diagram measurements have been the methods of choice in routine characterization of digital communication channels. The bit-error rate, however, does not provide insight into the digital channel's effect on transmitted signals, and in many situations the underlying assumptions behind eye diagram interpretation may not be justifiable. In order to supplement the conventional testing methods and improve upon their shortcomings, a general measurement tool has been developed to obtain direct statistical distributions of pulse shape parameters (distributions of the leading and trailing edge timing jitters and slopes, and the pulse peak heights) in addition to collections of severely degraded waveforms. The statistical distribution function contains a nearly complete picture of the noise process, which, in turn, reveals the mechanism of the noise generation process. Using this test setup, Gaussian time jitters of <;10 ps (FWHM) have been successfully measured.

Image reversal of positive photoresist: Characterization and modeling

We report on an investigation of a so-called image-reversal process where a negative tone image can be obtained with a positive resist. The reversal process is achieved by addition of a base to the exposed photoresist and a subsequent flood exposure. First, we characterize the image reversal by means of the characteristic curves, thus optimizing the process. A simple analytical model and a two-dimensional numerical simulation program have been developed in order to evaluate the dependence of the edge slope of the image-reversed resist line on resist and exposure parameters. Experimental investigation confirmed the simulation result that both positive and negative line edge slopes can be achieved with the image-reversal process by properly adjusting the exposure parameters. Finally, the image-reversal process has been compared experimentally to the standard positive process, considering linewidth control on profiled surfaces.

Snow loads in the 1985 National Building Code of Canada: Curved roofs

In the 1985 edition of the National Building Code of Canada (NBCC) the intensity of the specified snow load at any location on a roof is obtained by multiplying the ground snow load for the building locale by a series of factors. These factors reflect the overall reduction in average snow loads on roofs as compared with that on the ground, the effect of exposure to wind, the effect of roof slope, and the effect of drifting, sliding, creep, and drainage.The four loading cases for the design of curved roofs suggested in the Commentary on snow loads accompanying the 1980 NBCC were examined by determining, for roofs of circular cross section, the variation across the span of load intensity, shear force, and bending moment for a wide range of spans, ground snow loads, and roof edge slopes. The purpose of the examination was to fully describe known inconsistencies arising from these loading cases.A new case for drift loading was developed (case III) that, when used with "full" or "uniform" loading and with the unbalanced loading developed for the 1977 NBCC (case II), eliminates or at least reduces the inconsistencies. With this new loading case and the derivation of a formula to define when to switch from loading case II to the new case III the designer now has to consider only one unbalanced loading condition rather than three as before.A simplified method for establishing specified load intensities, shear forces, and bending moments, suitable at least for preliminary design, is also presented. Key words: bending moments, curved roofs, drifts, load intensity, shear force, snow load factors, wind.

Mesoscale and Convective-Scale Characteristics of Mature Hurricanes. Part I: General Observations by Research Aircraft

The analysis of instrumented aircraft data from four recent mature hurricanes reveals common mesoscale and convective-scale features. The structure and organization of the convection, precipitation, and wind flow are studied by combining the airborne observations, using basic instrumentation, with quantitative radar measurements. Three predominant precipitation features seen are 1) the eyewall, 2) a stratiform rain region adjacent to and outside the eyewall, and 3) rainbands that contain both convective and stratiform regions. The eyewall is so named because it surrounds the rain-free eye, but several additional features distinguish it from other convective bands in the hurricane. In particular the updraft, tangential wind maximum, and highest rainfall have preferred locations relative to each other, with the updraft being radially inward from the rain and wind maxima. The 10 dBZ radar reflectivity contour (indicative of the inner edge) slopes substantially outward with height, and there is evidence that the eyewall becomes more vertical with decreasing eye diameter. The inner eyewall edge is a region of cyclonic wind shear and substantial radial convergence. Of the four storms studied here, three had “double” eyewalls (concentric convective rings) during part of their lifetimes. The precipitation outside the eyewall is predominantly stratiform and is characterized by a “bright band” of enhanced radar reflectivity just below the melting level. Embedded within this uniform rain region an spiral and circular rainbands containing convective cells. Radar reflectivity is seen to decrease fairly rapidly with height above the 0°C level, even within the convective cores of the rainbands. Rainbands are distinguished from eyewalls by the absence of a pronounced tangential wind maximum, and the general lack of a consistently observed updraft location. Radar reflectivity maps of outer rainbands show a more “cellular” structure in the embedded convective elements when compared with eyewalls.

Quantitative evaluation of some edge-preserving noise-smoothing techniques

A quantitative evaluation of several edge-preserving noise-smoothing techniques is presented. All of the techniques evaluated are devised to preserve edge sharpness while achieving some degree of noise cleaning. They are based on local operations on neighboring points and all of them can be iterated. They are unweighted neighbor averaging (AVE), K-nearest neighbor averaging (KAVE), the edge and line weights method (EDLN), gradient inverse weighted smoothing (GRADIN), maximum homogeneity smoothing (MAXH), slope facet model smoothing (FACET), and median filtering (MEDIAN). The evaluation procedure involves two steps. First, the image is partitioned into regions based on the amount of spatial activity in a neighborhood of a pixel, where spatial activity is defined as local gradient. In the second part of the procedure an objective measure, the mean-square error, for each region of the partitioned image is obtained to evaluate the performance of the smoothing scheme at the corresponding level of spatial activity content. This evaluation procedure provides a convenient way to compare both the edge-preserving and noise-smoothing abilities of different schemes. The smoothing schemes were tested on a specially generated image with varying degrees of added noise and different edge slopes. The results of the comparison study are presented.

“Migration” of blowouts in seagrass beds at Barbados and Carriacou, West Indies, and its ecological and geological implications

Blowouts are grass-free depressions within seagrass beds at Barbados and Carriacou and reported in the literature to be common elsewhere in the Caribbean region. They are typically crescent-shaped in plan view with the convex side seaward, and are characteristic of elevated seagrass beds in regions of moderate to strong wave action. The seaward edge is steep and exposes rhizomes of Thalassia while the leeward edge slopes gently upward onto the seagrass plateau and is usually colonized by Syringodium. The general morphology of the blowouts, the zonation of organisms across them, and the existence at some blowouts of a lag deposit of cobble-sized material at the scarp base continuous with a rubble layer below the seagrass carpet suggested the blowouts “migrate” seaward. Measurements of erosion at the scarp and of advance of Syringodium onto the blowout floor over a period of one year confirmed this. It is estimated that in the region of blowouts any one point will be recurrently eroded and restabilized at intervals of the order of 5–15 years. Such processes limit successional development of the seagrass beds, disrupt sedimentary structures, and may result in deposits much coarser than those characteristic of the sandy seagrass carpet.