Magnification Changes Research Articles

Simulation of space charge neutralization using ions in electron beam projection optics

We have investigated, using Monte Carlo simulations, space charge neutralization using ions in a 4:1 telecentric doublet electron beam (e-beam) projection optics. The simulations were performed for two extreme conditions; one with ions moving at the same axial velocity as the e-beam, the other with stationary ions. For both conditions, global space charge effects; defocus, field curvature and magnification change are almost completely eliminated. Although the stochastic coulomb interaction is increased the total point spread which determines resolution can be decreased, because of the elimination of space charge induced spherical aberration. This suggests that space charge neutralization can reduce the global space charge effects without inducing unacceptable stochastic effects.

Effects of scanning resolution and digital image magnification on photostimulable phosphor imaging system

To examine the effects of changes in scanning resolution and digital magnification on the image quality and diagnostic ability of the photostimulable phosphor imaging system. Using a photostimulable phosphor imaging system, images of a human adult dried mandible phantom embedded in a 25 mm-thick epoxy resin block were made. The latent images on the photostimulable phosphor imaging plate were scanned using four different pixel sizes as follows: 25μm×25μm, 50μm×50μm, 100μm×100μm and 200μm×200μm. A primary image was produced for each pixel size. These images were also digitally magnified at powers of 2, 4 and 8 times. The gradient range, brightness and contrast of each image were adjusted to optimum levels on a cathode ray tube display, and hard copies were produced with a writing pixel size of 60μm×60μm. The granularity, sharpness and anatomical diagnostic ability of the images were assessed subjectively by eight dentists. Increasing the scanning resolution tended to generally improve image quality and diagnostic ability. Visual image quality was maintained up to a pixel size of 50 μm, and diagnostic ability was maintained up to a pixel size of 100μm. Digital image magnification degrated image quality, and more than 2-times magnification degraded diagnostic ability. Under the present experimental conditions, increasing the scanning resolution did not always lead to an improvement in image quality or diagnostic ability, and digital image magnification degraded image quality and diagnostic ability.

Overlay compatibility between two synchroton radiation steppers

A total overlay accuracy of less than 35 nm was obtained with two synchrotron radiation (SR) x-ray steppers developed by NTT and ASET. This value includes the pattern placement errors of two masks, errors due to the wafer etching process, and errors of two steppers that arise in exposure. The error factors affecting the overlay compatibility among SR x-ray steppers were analyzed using double-exposure experiments. The results show that the overlay error induced by the difference in runout between the two steppers was negligibly small and that the magnification change from shot to shot was caused by gap setting variations between the two steppers. These results demonstrate that a SR x-ray stepper can provide sufficient overlay compatibility for the 100 nm technical node and beyond.

Global space charge effect in SCALPEL

The global space charge (SC) effect in SCALPEL electron beam lithography system is investigated. First order properties of the SC lensing action (defocus and magnification change) in SCALPEL type projection systems are analyzed using a simple analytical technique. Aberrations induced by the lenses and SC in the projection optics are evaluated numerically using a Monte Carlo code developed to calculate the combined effect of Coulomb interactions and lens aberrations in the charge particle projection systems. We found that the defocus and the magnification change induced by SC are functions of two parameters, the beam perveance and the SCALPEL aperture size, that are critical for the system performance. The strong correlation identified between the best focus plane location and the aberrations induced by SC indicates that the SC lensing action can be effectively compensated by simply adjusting either the wafer plane position or excitations of projection lenses.

The Effect of Contact Lens Wear on the Central and Peripheral Corneal Endothelium

To compare central and peripheral corneal endothelial cell morphometry in normal subjects and long-term contact lens wearers. Endothelial cell density (ECD), coefficient of variation of cell area (CV), and percentage of six-sided cells were measured by contact specular microscopy in the corneal center and temporal periphery of both eyes of 43 long-term contact lens wearers and in 84 normal subjects who had never worn contact lenses. The latter group included 43 age- and sex-matched controls for the contact lens wearers. ECDs were corrected for magnification changes due to corneal thickness. Central ECD (2,723+/-366 cells/mm2, mean +/- SD) was significantly higher than peripheral ECD (2,646+/-394 cells/mm2) for the normal group (p = 0.01) but not for the contact lens wear group (2,855+/-428 cells/mm2 central, 2,844+/-494 cells/mm2 peripheral, p = 0.84). Peripheral CV was significantly higher than central for normal subjects and contact lens wearers and was significantly higher in both center and periphery in contact lens wearers than in controls. Central percentage of six-sided cells was significantly higher than peripheral for normal subjects and contact lens wearers and was lower in both center and periphery in contact lens wearers than in controls. Central ECD was significantly higher by 3% than peripheral ECD in normal subjects, but not in contact lens wearers. The results suggest that contact lens wear causes a mild redistribution of endothelial cells from the central to the peripheral cornea. A reversal of this redistribution after contact lens wear is discontinued for refractive surgery could mask mild central endothelial damage from the refractive procedure.

(Under)Graduate Teaching Using Internet Access to Electron Microscopes

Abstract The Lehigh University is presently offering direct access to top of the line electron microscopes at ORNL via the Internet for one graduate and one undergraduate course (Advanced TEM, Electron Microscopy & Microanalysis). The students at Lehigh have the opportunity to themselves control the Hitach HF-2000 FEG TEM. The controls presently include change of magnification and focus, moving the sample and correction for astigmatism. In this way, the students can collect high resolution lattice images of various materials and study e.g., the effects of changing focus on lattice images (contrast reversal). While the students at Lehigh can sit in the class room and run the instrument in broad daylight and communicate freely without disturbing the instrument by phonics, the instrument itself is protected from misuse through several layers of hardware and software. This new way of teaching EM courses has become possible through recent advances in computer hardware (live-time Fourier transforms (FFTs)) and software. A commercial software package TimbuktuPro provides remote access to the computer at the HF-2000 at ORNL which controls the instrument as well as the slow-scan CCD-cameras (Gatan, model 794) attached to the instrument.

Analysis of stencil mask distortion in ion projection lithography

Accurate feature placement on the wafer in ion projection lithography requires that the distortion due to stress relief produced by the pattern of holes in the mask be controlled. We have used the finite element method provided by the ANSYS software package to calculate the two dimensional mask distortion due to non-symmetrical patterns of openings in stencil masks and to analyze a method for controlling distortion. The ion projection lithography mask is a circular silicon membrane 120 mm in diameter 2.5 μm thick rigidly held around the perimeter. The central 60 × 60 mm square area will contain the pattern to be printed, demagnified by 3x. We take the intrinsic stress of the membrane to be 10 MPa, the Young's modulus of the membrane to be E = 1.5 × 1011 Pa and the Poisson ratio ν = 0.17. We have explored the x-y distortion produced by various simple geometries. For example, consider an asymmetric grid of square holes which is 22% open on one half and 10% open on the other half. High distortion in this case will occur along the diameter, between the two halves. The boundary between the two halves (along the diameter) is bowed by 182 nm.A method for reducing the distortion is to cut a pair perforation rings along the perimeter. The perforation rings will have the effect that the central part of the membrane will have the stress relieved and it will be held in effect by “springs” at a constant, low stress level. We have calculated that the bow of the diameter can be reduced to 18 nm by a suitable geometry of the perforations. The perforation ring is an effective means of reducing distortion to well below an acceptable level. The uniform shrinkage of the pattern due to stress relief is simply a small change in magnification which is automatically corrected by the beam lock in the ion optical column.

The fractal behaviour of triangular refined/derefined meshes

SUMMARY In the paper the author presents a novel point of view for the refinement and derefinement algorithms of triangular nested meshes using fractal concepts and iterated function systems (IFS). The fractal behaviour can be understood in the sense that these meshes feature a remarkable amplifying invariance under changes of magnification. Here we compare the meshes obtained by the combination of these algorithms with those presented by Bova and Carey (1992). Although both of the meshes are very similar, the current algorithms automatically build and manage sequences of nested irregular discretizations of the domain. The author illustrates here how the application of IFS families is equivalent to the use of an adaptive strategy that combines the refinement procedure with the derefinement one.

The fractal behaviour of triangular refined/derefined meshes

In the paper the author presents a novel point of view for the refinement and derefinement algorithms of triangular nested meshes using fractal concepts and iterated function systems (IFS). The fractal behaviour can be understood in the sense that these meshes feature a remarkable amplifying invariance under changes of magnification. Here we compare the meshes obtained by the combination of these algorithms with those presented by Bova and Carey (1992). Although both of the meshes are very similar, the current algorithms automatically build and manage sequences of nested irregular discretizations of the domain. The author illustrates here how the application of IFS families is equivalent to the use of an adaptive strategy that combines the refinement procedure with the derefinement one.

Emmetropization and optical development of the eye of the barn owl (Tyto alba)

1. We have studied the development of the refractive state in young barn owls (Tyto alba pratincola). Strikingly, the eyes had severe refractive errors shortly after lid opening (which occurred around day 14 after hatching; average from 6 owls: 13.83 ± 1.47 days). Refractive errors vanished in the subsequent one or two weeks (Fig. 1, Fig. 2). 2. Refractive errors did not differ by more than 1 diopter (D) in both eyes of an individual (Fig. 2). Thus, non-visual control of eye growth was sufficient to produce non-random refractions. However, visual input was finally required to adjust the optical system to emmetropia. 3. Using in-vivo A-scan ultrasonography of ocular dimensions (Fig. 4A), photokeratometric measurements of corneal radius of curvature (Fig. 4B), and frozen sections of excised eyes (Fig. 3), we developed paraxial schematic eye models which described age-dependent changes in ocular parameters and were applicable through the ages from lid opening to fledging (Table 1). A schematic eye for the adult barn owl (European subspecies: Tyto alba alba) is also provided. Eye sizes in an adult owl of the American (Tyto alba pratincola) and the European subspecies (T. alba alba) were similar despite of different body weights (500 g and 350 g, respectively). 4. The schematic eyes were used to test which ocular parameters might have caused the recovery from refractive errors. However, none of the ocular dimensions measured underwent obvious changes in their growth curves as visual input became available. Apparently, coordinated growth of several ocular components produced emmetropia. 5. From the schematic eye model, the developmental changes in image brightness and image magnification were calculated (Fig. 5). In barn owl eyes, image size was not quite as extreme as in the tawny owl or the great horned owl. However, the image was larger and the f/number was lower than in diurnal birds of comparable weight (pigeon, chicken). The observation supports a conclusion that image size is maximised in owls to permit a higher degree of photoreceptor convergence for higher light sensitivity at dusk while spatial acuity remains comparable to diurnal birds with smaller eyes.

Motor and somatosensory corticostriatal projection magnifications in the squirrel monkey.

1. Motor and somatosensory cortex project massively to the primate striatal matrix, terminating in distributed sets of overlapping projection zones (matrisomes) within the putamen. To study this system quantitatively, we have developed a computer-assisted estimation of the changes in magnification that occur as motor and somatosensory cortical body representations are projected onto the putamen. 2. Cortical and striatal body maps were assessed in squirrel monkeys by injecting anterograde tract tracers into electrophysiologically identified body-part representations in cortical areas 4, 3a, 3b, and 1. Relative projection magnification was defined as the ratio of the cortical injection site volume to the striatal projection site volume. 3. Magnification comparisons indicate that the tracers wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and 35S-methionine have similar sensitivities. 4. The relative proportions of body-part representations in the striatal maps were not significantly different from those in cortical maps. Both had large representations of hand, foot, and mouth, and smaller representations of trunk. 5. The relative magnification of the motor cortex projection to the striatum was roughly twice as large as those of projections from individual somatosensory areas. 6. These findings suggest that, in the sensorimotor striatum, motor and somatosensory inputs may undergo different proportions of local processing at the borders of their distribution zones (striosomes and matrisomes).

1321 Defocus induced ametropia in chicks - role of magnification and orbital changes

1321 Defocus induced ametropia in chicks - role of magnification and orbital changes

Defocus induced ametropia in chicks - role of magnification and orbital changes

Defocus induced ametropia in chicks - role of magnification and orbital changes

Conditions for Electron Tomographic Data Acquisition

The conventional algorithms employed in electron microscope tomography require that the series of images obtained from different orientations of the specimen each represent a parallel orthographic projection under uniform magnification. Electron microscope optics can produce distortions in images that may affect the accuracy of a tomographic reconstruction. These distortions result in images with differential rotation and magnification of regions of a thick or highly tilted specimen located at different distances with respect to the plane of focus. The distortions increase in magnitude and may significantly affect the accuracy of the tomographic data when images are acquired under current center misalignment or non-eucentric positioning of the specimen. An additional source of error can be introduced if the condenser lenses are adjusted to compensate for the intensity attenuation due to the increased beam path length as the specimen is tilted. The change in beam crossover position due to adjustment of the condensers alters the beam divergence and may introduce systematic changes in magnification over the tilt series. The process of alignment of the tilt series will propagate these errors to more central regions of the image. In most cases, with proper consideration, it is possible to minimize these errors to levels where they will have negligible effects on the resolution of the tomographic reconstruction.

A Computer-assisted Plankton Analysis System for the Macintosh

CAPAS (Computer-assisted Plankton Analysis System), an application software developed for Macintosh computers, was designed for the analysis of taxonomic and size composition of zooplankton. We based CAPAS on the zooplankton analysis system of Mills and Confer (1986), but instead of using electronic calipers, CAPAS requires a digitizing surface for making one-dimensional plankter measurements. Advantages of CAPAS over Mills and Confer's system (1986) include (1) freedom from caliper-associated mechanical error; (2) increased flexibility regarding sample magnification changes, taxonomic lists, measurable size ranges, precision level, and output format; and (3) increased file editing abilities. Moreover, prey taxon- and size-dependent selectivities (Manly-Chesson preference index α and Strauss's linear index L) of planktivorous predators can be calculated using plankton samples from an “environment” (e.g., lake, pond, tank) in which a predator was feeding and samples from either the predator's stomach or from the “environment” after the predator had been feeding. Though designed primarily for the analysis of zooplankton, CAPAS can be useful in a variety of other analyses in which taxonomic or size composition is needed (e.g., phytoplankton enumeration, measurement and enumeration of morphological characteristics of zooplankton such as leg spines and setules, antennae segments, etc.).

Wide-screen autostereoscopic display system employing head-position tracking

We propose a head-tracking autostereoscopic display system based on magnetic-sensor tracking of the viewer's side-to-side location, and optical slewing of a stereoscopic image-pair array projected onto a lenticular screen so as to keep the images received by the viewer's eyes distinct. Viewer distance changes are accommodated by slight magnification changes of the projected image array. A high-definition-TV LCD projector is used with a 178-cm (70-in.) lenticular sheet (diagonal measurement) to provide impressive computer-generated 3-D images over a particularly wide viewing zone. The system finds application in a virtual-space teleconferencing system that requires a large-scale stereoscopic display without the use of special viewing glasses.

Alterations of the cortical representation of the rat ventrum induced by nursing behavior

The representation of the surfaces of the trunk was mapped in detail in a series of anesthetized adult female rats to assess cortical representational changes that might be induced in the SI cortical field by a major natural source of a differentially heavy schedule of tactile inputs: the stimulation of the rat ventrum in nursing behavior. Controls included virgin rats and postpartum age-matched rats whose litters were removed on the day of birth. The SI representation of the ventral trunk skin of lactating rats was about 1.6 x larger than in matched postpartum nonlactating or virgin controls. The greatest representational change--about twofold--was for the nipple-bearing skin between the forelimbs and hindlimbs. Indeed, changes in SI representational territory for the middle third of the ventrum, a skin zone without nipples, were not significant. As a rule, the representation of the ventrum skin in lactating rats was at least as topographically ordered as was that reconstructed for nonlactating postpartum and virgin controls. Receptive fields (RFs) representing the ventrum skin in lactating females were about one-third the sizes of those recorded in matched nonlactating or virgin controls. RF size differences were again greater for the representation of the nipple-bearing skin in the anterior and posterior thirds of the ventrum than for the central third. Changes in RF sizes were roughly inversely related to changes in the cortical magnification of representation of the ventrum on the proportion of about 3:2. Interestingly, the glabrous nipple and areolar skin were only weakly represented--or not demonstrably represented--in the SI map of either lactating or control rats. These results indicate that there is a largely unstudied cortical neurology of nursing behavior. Major CNS changes are induced by this dramatic, episodic change in behaviorally important tactile inputs. In turn, input-induced changes presumably contribute to this emergent, rapidly evolving behavior.

Detection and discrimination of curvature in foveal and peripheral vision

Curvature detection and discrimination were measured across the visual field in order to determine whether performance at a given eccentricity could be related to that at another by a simple change of magnification. Both types of task obeyed this concept, the critical variable being the rate at which magnification must increase as a function of eccentricity. The situation can be expressed in terms of the eccentricity (E2) at which magnification must be doubled to retain performance equivalent to that at the fovea. E2 values were 1.84-1.96 deg for the detection task and 1.42-2.27 deg for discrimination. These are similar to E2 values for vernier acuity and orientation discrimination, suggesting that all of these tasks share a common determining feature across the visual field, perhaps the distribution of neural elements selective for stimulus orientation.

Magnification and visual acuity in refractive surgery.

In comparisons of retinal image size within the same eye before and after refractive surgery, a change in the plane of correction from the spectacle to the cornea induces a change in retinal magnification. Comparing retinal image size between eyes of different individuals, a change in the plane of correction as well as the type of ametropia (axial or refractive) interacts to change the retinal magnification. Consequently, comparing acuity before and after refractive surgery without considering the effects of retinal magnification can be misleading. Magnification effects can be large, accounting for a visual acuity increase of 1 line or more. Here we model the magnification induced by refractive surgery in various reference eyes and discuss implications in the context of current clinical trials.

The influence of focal spot size on image resolution and test phantom scores in mammography.

This paper reports an experimental investigation of the extent to which focal spot size influences image resolution in mammography. Films of two different phantoms, both containing high contrast bar patterns, were obtained using three different foci from 0.9 to 0.1 mm, and three degrees of magnification with the smallest of those foci. Some influence of focal spot size was detectable in all films except for the 0.1 mm focus at low magnification, where it was negligible in comparison with film-screen unsharpness, but effects attributed to the film-screen system were more important than focus size except with the 0.9 mm focus or at high magnification. However, a nominal 0.4 mm focus may have an effective size of 0.9 mm close to the chest wall side of the film. These two phantoms, and two others, were used to investigate the changes of perceptibility of "realistic" details, all of which depend on a combination of contrast, resolution and noise, with changes of focal spot size and magnification. As expected, when judged in this way image quality improved as focal spot size decreased. With the fine focus it also improved as magnification increased, unlike changes in high contrast resolution which decreased for high magnification. Thus conventional bar patterns are not always a good guide to detail perceptibility in mammograms, where the effects of noise may be as important as those of focal spot size.